27 Sep

My Post-Summer Research Reading List

In The myths and physiology surrounding intrapartum decelerations: the critical role of the peripheral chemoreflex published in the Journal of Physiology, Lear et al have written a highly readable and methodical analysis of current evidence about the mechanisms of fetal heart rate decelerations. This is a must read for anyone seriously using fetal monitoring. He challenges long held tenets and presents a simplified coherent approach to the interpretation of heart rate monitoring. Here are two excerpts that may compel you to read further:

“… Despite multiple detailed analyses, there is no consistent FHR marker of fetal compromise …”

“… We believe that it is better to focus on the frequency, depth and total duration of decelerations during labor rather than on timing, shape or supposed aetiology of the specific deceleration.”

In an article published recently in the American Journal of Obstetrics & Gynecology titled Triggers, bundles, protocols, and checklists — what every maternal care provider needs to know, Arora et al define and provide examples of various methods to standardize and streamline clinical care and summarize the evidence supporting their association with improved outcomes. Many examples are provided for obstetrical issues such as hemorrhage, hypertension, oxytocin usage or preop preparation. With burgeoning evidence from diverse medical and non-medical domains, the question is no longer “Do these methods work?“, but rather “How can we get wider adoption and sustain compliance?” In short, how do we actually change established clinical beliefs and behaviors? This article is less informative on these practical issues.

InfluencerThere is abundant data about effective ways to change behavior. In short, behaviors will not change without aligning a critical mass of influential factors. Determination and good intentions alone are insufficient and depending upon them alone is destined to fail. To supplement this review of available obstetrical safety packages we strongly recommend the book- Influencer: The New Science of Leading Change, Second Edition by David Maxfield, Ron McMillan, Al Switzler. (Click here to see a summary of this excellent work)

22 Sep

Being a FHR Tracing Me Too

How many labor & delivery nurses NEVER ask for a second opinion when interpreting a tracing?  If you do, is that a bad thing?FHR Interpretation AgreementWe ask because it turns out that a fair amount of research says that labor nurses SHOULD ASK for a back up opinion. Multiple research studies show that agreement about FHR tracing interpretation is a pretty rare event.

Discover what this research tells us and how some of today’s leading OB clinicians are using technology tools to gain a valuable second opinion before they make important care decisions. Register for a free webinar on Sept. 28th, Noon – 12:30 PM ET

Click to register today

11 Aug

Part 3: Perinatal Nursing & Technology

Rebecca Cypher, PeriGen Chief Nursing OfficerPart 3:
Perinatal Nursing & Technology
Time to Accept & Embrace the Challenge

by Rebecca Cypher, MSN, PNNP
Chief Nursing Officer, PeriGen

I hope you enjoyed the first two excerpts from my recent white paper on technologies in perinatal nursing. This article, done on request by PeriGen (the electronic fetal monitoring software firm for which I serve as Chief Nursing Officer), looks at how technology has evolved in response to changes in perinatal nursing, how we in turn have changed as a result of electronic FHR monitoring, and a view to how we as nursing professionals can influence continued improvement in perinatal technologies.

Below is the final excerpt where we examine the importance of a perinatal nurses view on technology improvements. In case you missed the first two installments, PeriGen has posted the full article as a PDF here.

Why Should Nurses Care?

Between 2008-2012, there were 2.8 million registered nurses (including advanced practice nurses) in the United States workforce making nursing one of the largest health-related professional groups. 24, 29, 30 According to Gallup polls, these professionals are regarded by the public as the most trusted in the United States. Nursing is a caring profession that requires licensure, knowledge and clinical skill. Nursing demonstrates the best side of humanity. Well-designed HIT augments nursing capacity. Nurses must be clear in thinking and understanding the relative strengths and limitations of all parties in order to direct the evolution of these technologies. In turn, nurses can harness these technologies to support the mission of providing high quality patient care that is evidence-based, individualized, efficient and safe.

Government agencies expect a 21% increase in demand for nurses nationwide by 2025 though considerable variation of supply and demand at the state level is anticipated. Nursing employment will continue to be affected by factors including population growth, a shift in demographics as the median age increases, economic conditions, employment and retirement of nursing personnel and changes in health care reimbursement. Workforce projection models demonstrate that the rapidly changing health care delivery system, which includes HIT, is shifting how patient care is delivered and the specific role the nursing workforce plays in these changes. 31

Perinatal nurses are using technology in conjunction with clinical knowledge that has been accumulated through hands on experience and education. This combination assists in improving care and facilitates multidisciplinary communication. Technology allows nurses to ask the right questions at the right time, perform streamlined nursing assessments, accurately determine a correct diagnosis from a multidisciplinary approach, and perform appropriate tasks and intervention on the front and back end of decision-making processes. 32


In this modern era, technology is commonplace whether it’s embedded in households, communication methods, modes of transportation or healthcare. In these areas technology continues to be created, refined and updated on a regular basis. Advances in technology, whether it’s a new cellular phone model or component of medical equipment, are requisite in order to provide and improve efficiency, convenience, accessibility and safety. As nurses provide day to day quality patient care in the perinatal setting, technology will continue to influence many facets of the nursing process framework. In today’s healthcare environment, few perinatal nurses can envision delivering patient care without assistance from some form of technology, whether that technology be an automatic blood pressure machine or fetal surveillance with an electronic fetal monitor. Nursing is what we as individuals do best and nurses working in conjunction with HIT is clearly an investment in optimizing efficiency, perinatal outcomes and patient safety. Throughout time women in labor have sought assistance from others with experience and skills. Clearly nurses will continue to fill that essential role backed by increasingly complex technology as HIT evolves.

To continue reading this article or review the references, please click here

04 Aug

Part 2: Perinatal Nursing & Technology

Rebecca Cypher, PeriGen Chief Nursing OfficerPart 2: Perinatal Nursing & Technology
Time to Accept & Embrace the Challenge

by Rebecca Cypher, MSN, PNNP
Chief Nursing Officer, PeriGen

You may remember that I shared the first part of my recent white paper with you not too long ago. It examined how healthcare technology as evolved as a result of perinatal nursing needs and changes in standards. Now it’s time to look at the flip side: How nursing as changed as a result of technology, specifically systems that help us monitor FHR.

PeriGen has also made the full article available as a PDF here.

Clinical Acumen and Care

While the fundamental technology in standard fetal monitoring equipment has changed little in recent decades, clinical behavior in response to FHR monitoring has changed considerably. Clearly defined nomenclature, 10, 11 standardized clinical guidelines, 12-16 and structured communication techniques are now part of obstetric care. Moreover, published nursing position statements and other resources have highlighted that skilled clinicians are essential to ensure maternal and fetal well-being when fetal monitoring is utilized. Additional publications focus on HIT’s vital healthcare role in terms of enhancing opportunities for reducing error in perinatal settings. 3, 11, 17, 18

There is increased awareness that environmental and human factors can impair clinical judgment resulting in delayed intervention and birth-related injury. To address some of these issues healthcare professionals have:

  • Legislation that limits working hours
  • Updated recommendations on nurse-patient ratios
  • Stricter and more frequent credentialing
  • Chain of command procedures
  • In-house coverage rather than on-call at home

Despite these measures, assessing a clinical situation is still challenging. Nurses must often project what will happen in the future. Furthermore, these same nurses prefer to avoid allowing patients to deteriorate to a suboptimal status because, once changes have occurred, safe recovery may be impossible. To make decisions, the clinical mind must focus on what is important and disregard the irrelevant. The human brain is vulnerable to well described biases in this task.

Recent “vivid” experiences affect individual’s perception of risk. The psychological phenomenon of “Tunnel Vision” refers to a tendency to perceive and confirm only the information that aligns with a particular viewpoint and discard contradicting information. 19 Variations of this phenomenon include “Wishful thinking.” For example, a belief that a patient will deliver soon or not deteriorate on a shift can lead to poor FHR tracing assessments which is inconsistent under the best of conditions. Occasionally, humans get tired, distracted, have memory lapses, take risky shortcuts, or get diverted by competing interests. Furthermore, inadequate training or clinical experience can compound problems at the bedside. The objective, unbiased, statistical methods offered by HIT can counter these types of human bias, reduce information overload and assist novice and seasoned nurses to make more confident decisions. 20, 21, 22

Another attractive HIT feature for perinatal leaders is the ability to collect and organize outcome and performance data such as the number of cesarean births or elective inductions. Instead of hand counting data from multiple sources, which takes up valuable nursing time and resources, HIT can collect this data and provide written reports on a regular basis. Performance can be compared over time, to other unit level quality improvement goals or datasets of core measure such as those established by the Joint Commission and the National Perinatal Information Center. Policies and procedures can then be further refined based on benchmarked data in order to provide safer care to patients. 18, 23

The divisions between fetal monitoring technologies, technologies in healthcare information and modern nursing care have been become increasingly blurred. Monitors contain software. Systems in HIT employ clinical algorithms. Clinical algorithms are often based on research using huge datasets derived from HIT systems. Clinicians make decisions on monitoring data and research findings. A brief comparison of strengths and weakness related to computer and human faculties is outlined in Figure 2. Both are fallible but each one has strengths in specific areas. The strengths of one counter weaknesses of the others. Computers crunch numbers well. Let the computers apply that capacity to analyze, organize and display critical information without bias so that nurses can be empowered to use technology and focus on higher order clinical reasoning, collaborative dialogue with colleagues and compassionate quality care. Surely valuable nursing time should not be consumed by the repetitive, manual labor of measuring, counting and calculating. On the other hand, nurses are essential to seek out and integrate information from additional sources, see exceptions to the general rule, cue in to unspoken patient fears, and even make do with missing data. Nurses communicate, reason, educate, encourage and empathize with patients and families. The profession makes a profound difference as hands-on patient contact, visual interpretation at the bedside and having an underlying basic foundation in obstetric care is absolutely necessary to validate HIT information. The perception that technology will take over nursing responsibilities, such as FHR interpretation, leaving all data to be interpreted, documented and managed by artificial intelligence is not only incorrect but illogical. However, given what is known about human error, surely one could not advocate for one approach without the other i.e., nurses without equipment or equipment without nurses.

As HIT related to antepartum and intrapartum fetal surveillance techniques evolve, the profession is often concerned with how to integrate them without challenging or devaluing the role of nursing. This is where an understanding of HIT strengths is important so that they can insist on HIT functionality that is truly helpful allowing nurses to have more time with patients. Perinatal nurses must continue to be involved in the design of state-of-the art systems at the bedside that optimize time for hands-on patient care and streamlined workflow and patient safety. 18, 24 Additionally, nurses play an important role in collaboratively developing and utilizing a variety of quality improvement and risk reductions strategies with the aid of HIT to improve patient care, reduce adverse perinatal and neonatal outcomes (e.g. emergent cesarean section or neonatal intensive care unit admission) and potentially reduce liability. 13,25-28 These include but are not limited to

Developing clear fetal monitoring guidelines that include multidisciplinary protocols for interpretation, intervention, and documentation

Educating nurses, residents, nurse midwives, and physicians on fundamentals of fetal monitoring using standardized fetal monitoring nomenclature

Applying HIT to patient care by using high quality up to date decision aids, bundles and toolkits

Implementing peer reviewed evidence based information, such as clinical protocols, checklists (i.e. oxytocin), and guidelines in a high reliability organization to reduce clinician practice variation

To continue reading this article or review the references, please click here

28 Jul

Part 1: Perinatal Nursing & Technology

Rebecca Cypher, PeriGen Chief Nursing OfficerTechnologies in Perinatal Nursing:
Time to Accept & Embrace the Challenge

by Rebecca Cypher, MSN, PNNP
Chief Nursing Officer, PeriGen, Inc.

I wanted to share with you a white paper that PeriGen asked me to prepare on how today’s healthcare technologies can help us in perinatal nursing. Since the paper is lengthy and few of us have time to read such articles in one sitting, I’ve split the paper into three parts and will deliver it to you via email and PeriGen’s social media platforms (Facebook, LinkedIn, Twitter) over the next several weeks. If, by chance, you would like the full article, click here for access to the PDF

Let’s start with a look back at where we’ve come from:

Humans have a long history of inventing tools to survive and achieve goals more efficiently.1 Some tools survive the test of time and evolve while others are abandoned. Healthcare is no different. Monitoring devices and healthcare information technologies (HIT) are key tools used in modern healthcare and time will tell how well they advance as healthcare changes.

Perinatal Nursing Technology-Figure 1Perinatal nursing is just one example of where HIT has had a significant influence on integrating technology with a nursing process framework. 3 Monitoring technology, information technology and clinical acumen can be thought of as an interdependent hierarchy. (See Figure 1 above ). For example, at the most basic level, electronic fetal monitor (EFM) sensors measure fetal heart rates (FHR) and uterine activity. At an intermediate level, HIT consolidates and analyzes the monitoring data for clinicians. At the highest level, nurses decide what the data means, what is likely to happen next and implement the most beneficial interventions. Each level depends, in part, upon the former. Historically, nurses did everything including auscultating FHRs with a fetoscope, palpating uterine activity, recording data in a paper record, and made FHR decisions based on what could be heard and recorded. Now EFM and software accomplish several of these tasks. For some nurses, these new technologies evoked insecurity, a feeling that professional value and roles would be diminished. For others, new technology provided a release from endless listening, counting and transcribing and consequently freeing time to focus on clinical judgment and hands on patient care. In fact, while fetal monitors did reduce the counting tasks they also elevated the expectation for medical reasoning or tracing interpretation.

The purpose of this document is to broadly outline the evolution in each of the three levels of data collection via monitors, interpretation and clinical intervention. In addition, we will discuss relative strengths and weakness of clinicians and HIT in the context of modern perinatal care and how they complement each other.

Clarity on this subject is important to:

  1. Emphasize that clinical acumen for diagnostic and therapeutic decisions and compassionate care is paramount
  2. Determine where and why technology can be a help or a hindrance for nurses
  3. Provide guidance for designers of new technology to meet a nurse’s greatest clinical need

Monitoring Technology

By 2004, 89% of births in the United States were monitored electronically. 4 In view of the high and stable rate of electronic monitoring Vital Statistics ceased reporting EFM utilization rates in annual birth-related reports. Monitoring sensors and signal processing have evolved to provide excellent measurement of FHR, uterine activity and maternal vital signs. 5 Fetal monitors can indicate signal coincidence when two sources of heart rate measurement are the same. On the other hand, monitoring faces new physical challenges. Obesity impedes monitoring by Doppler ultrasound based external sensor technology.

Given the imprecise relationship between FHR and fetal brain oxygenation or acid- base status, a considerable effort has been devoted to finding other physiological measures that would be more discriminating. Unfortunately, prospective clinical trials show no clinical benefit in using EFM with additional sensors that measure fetal oxygen saturation or fetal ST segments of the fetal ECG compared to using EFM alone. 6, 7 Thus, for the near future, the obstetrical world remains dependent upon standard EFM.

Healthcare Information Technology

HIT has evolved considerably in contrast, to the relative stagnation of the monitoring devices. Early electronic medical records allowed clinicians to collect, display and store information in a legible fashion, but at considerable inefficiency. Data entry was often arduous, time-consuming and error -prone. “Cut and paste” shortcuts led to nonsense entries with costly legal repercussions. Lack of interoperability wasted time with redundant documentation.

Perinatal nurses have played an important role in this evolution. Working alongside HIT experts, nurses have been vital members of multidisciplinary teams in which integrating, implementing, and maintaining fetal surveillance technologies with clinical practice has become a priority in patient centered care and safety. This is especially apparent in organizations that promote high reliability units.

There has been considerable industry consolidation on a few types of hospital-wide electronic medical records boosting interoperability. IT networks, smartphones and cloud-based computing give nurses unprecedented and speedy access to information and human expertise. The computational power and reliability of basic computers and networks means very complex analytical methods can be available in real-time at the bedside. 8, 9 Computerized analyses can now be applied to EFM tracings or evaluate labor progression to bring consistent interpretation, reducing clinical variation.

Psychological testing has underlined the importance of simplicity and clarity of information displayed on computer screens. Overcrowded or confusing displays can lead to medical error. Better graphical designs mean critical information is consolidated for efficient review by clinicians. High rates of false alarms lead to frustration and disregard of the device. Truly discriminating alerts based on better evidence-based algorithms alleviate this alarm fatigue.

To continue reading this article or review the references, please click here

10 Mar

Free L&D Training Session

Register for WebinarThe following is this week’s excerpt from The Physiology of EFM.  Hear author Emily Hamilton review the entire contents of this white paper during the free online training webinar designed for labor & delivery clinicians on March 16th (Noon – 12:30 PM ET).

Register today for free L&D training session
The Physiology of EFM

Wednesday, March 16th
Noon – 12:30 PM ET

Fetal Heart Rate Variability

Current clinical guidelines that classify tracings rely heavily on reduced baseline heart rate variability as an indicator of significant acidosis and/or need for intervention.6-12 Minimal variability, especially when it persists and is accompanied by decelerations, is associated with marked acidemia, low Apgar scores and hypoxic injury.

Minimal variability, especially when it persists and is accompanied by decelerations, is associated with marked acidemia, low Apgar scores and hypoxic injury.

All of the mechanisms controlling fetal heart rate depicted in Figure 1 influence heart rate variability. Fetal behavioral states, breathing and movements affect heart rate variability acting though the central pathways to the medulla, and then to the heart via the sympathetic and parasympathetic systems. Fetal heart rate variability is suppressed by factors that depress fetal brain function.

Animal experiments have shown that blockage of the parasympathetic system with atropine results in a reduction in short-term variability.13 A reduction in long-term variability occurs after sympathetic blockade.14, 15 Fetal heart rate variability is more than the simple “push-pull” interactions between the inhibitory and acceleratory limbs of the autonomic nervous system. The heart itself contributes to variability. Even with complete double blockade of the sympathetic and parasympathetic systems, around 35-40% of fetal lamb heart rate variability persists.13 A clinical demonstration of the intrinsic rhythmicity of the heart is found in transplantation surgery. An excised heart continues to beat and demonstrate heart rate variability.

Marked variability may be a sign of activation of compensatory pathways.

The association between variability and metabolic acidosis is less clear. This is important because all contemporary EFM classification methods place high reliance upon baseline fetal heart rate variability to exclude the presence of metabolic acidosis.6-12 The 2008 NICHD Update publication in which the Category I, II, III classification method was first described includes a statement that “moderate variability reliably predicts the absence of metabolic acidemia at the time that it is observed.”6 This concept was softened in the 2009 ACOG Practice Bulletin 106 with the statement “The data relating FHR variability to clinical outcomes, however, are sparse.”7 This practice bulletin endorsed the 3-level categorization of tracings where the third level required absent baseline variability.

The 2010 ACOG Practice Bulletin 116 presented a clinical management algorithm with high reliance on moderate variability.8 In this management algorithm, the recommendations for tracings in Category 2 were continued surveillance and intrauterine resuscitation measures, as long as there was moderate variability. Only a failure to respond to intrauterine resuscitative measures in the presence of absent or minimal variability lead to the recommendation of “consideration of delivery” for Category II tracings.

There is a growing body of literature that does not support the statement that moderate variability reliably excludes the presence of metabolic acidemia.

In animal studies, vascular instrumentation allows for blood gas measurement at any specific time to be correlated with the coexisting fetal heart rate features. Martin demonstrated that in sheep the initial fetal heart rate response to sudden hypoxemia was a slowing of the heart rate with increased variability.1 Others observed similar changes in sheep and in monkeys.16-18 Field et al found initial decreases in heart rate variability with iliac occlusion in sheep, but variability returned to normal by 36 minutes despite worsening metabolic acidosis.19 These observations of normal variability in the face of acidemia led researchers to postulate that some aspect of variability control could be different in animals compared to humans.

In the human literature, four recent and independent studies using various definitions of acidosis and examining the last 30-60 minutes of the tracing reported that the percentage of babies with acidosis who had moderate variability ranged from 15% to 91%.20-23 Even with near lethal levels of uterine artery base deficit (>=16 mmol/L), a full 15 to 32% of these babies had moderate baseline variability in the tracing recorded just before birth.20, 21 Another study examined baseline variability in term babies who required supplemental oxygen for more than 6 hours or mechanical ventilation.24 In this study, marked variability in the last 30 minutes was significantly associated with these respiratory morbidities. Minimal variability was not. This finding is in keeping with other direct observations on the correlation between increased heart rate variability and catecholamines concentration on non-acidotic term fetuses.25 It appears that marked variability may be a sign of activation of compensatory pathways.

10 Mar

Best practices for High Reliability

best practices for high reliability in obstetricsUsing their extensive experience in implementing approaches to promote efficiency and high reliability in health care, the team of obstetric leaders who collaborated to author the recently released eBook A Vision of the Future of Obstetrics identified five key clinical best practices.  Here they are in summary:

Best practices for obstetric units

  1. Select a reasonable process
  2. Analyze and modify
  3. Target critical behaviors
  4. Clarify and define
  5. Choose wisely

The free eBook details clinical processes, developed by leading health systems, to execute these broad principles.

What practices is your hospital or health system using to improve efficiency and high reliability in labor & delivery?

Click to continue reading eBook in the Apple Store or as a PDF

01 Mar

Research on Late FHR Decelerations

The following excerpt is taken from The Physiology of EFM, a PeriGen white paper written by Emily Hamilton, MDCM and Philip Warrick, Ph.D. Its contents are among the topics to be covered at the free March 16th lunchtime labor & delivery training webinar.

Click Here to Register | Space is Filling Fast

Late Fetal Heart Rate (FHR) Decelerations

Two pathways are involved with late fetal heart rate decelerations

Figure 3: Two pathways are involved with late decelerations, adapted from Martin 1979 (1) and Freeman et al. (2)

To simulate decreased uteroplacental oxygen delivery, Martin applied repeated hypogastric artery occlusions in sheep. These occlusions resulted in fetal hypertension which was followed by vagally mediated decelerations. The degree of hypertension and the amount of deceleration were closely related, although some deceleration remained when the transient hypertension was prevented by alpha-adrenergic blockade. The timing of the onset, nadir and end of the deceleration was delayed with respect to the occlusion and mirrored the timeline of the hypertensive response. Vagal blockade eliminated these decelerations in the non-acidemic sheep. Thus, “intermittent placental insufficiency” can cause decelerations and its effects are mediated by the vagus nerve. These “late” decelerations were not associated with fetal acidosis. 1, 3

When the occlusions were extended to produce fetal acidosis, the fetal hypertensive response lost its progressive character, reaching a plateau early after the beginning of the occlusion, while the deceleration continued to fall with its nadir occurring at or after the end of the occlusion. With progressive acidemia the decelerations became deeper and longer. In the presence of very severe acidemia (pH=6.96) they could not be eliminated by vagal blockade. With complete vagal and alpha and beta adrenergic blockade, the decelerations persisted. The fetal heart, devoid of any sympathetic and parasympathetic influences, showed decelerations suggesting that intrinsic myocardial depression was the deceleration mechanism in the presence of severe acidosis and hypoxia.3

Although the individual pathways described above cover the major mechanisms of fetal heart rate decelerations, the actual situation is more complex. Even in the sheep experiments using precisely controlled conditions, consistent fetal heart rate decelerations could not be produced equally in all animals despite 2 hours of repetitive maternal vascular occlusions.3

25 Feb

Share the Vision | Excerpt

Obstetrics challenge - standardization of care


Our OB 3.0 team of thought leaders focused on two key challenges for obstetric patient care.  The first, covered in Section I of the new ebook A Vision of the Future of Obstetrics is standardization of health care.  Here’s an excerpt:

Issues preventing

Standardization of Care

The quest for exciting and game changing approaches to solve today’s medical problems is appealing.  However, not only are such miracles seldom found, but experience shows that much improvement can be gained by applying existing best practices uniformly. 7-9   Across all large endeavors, such uniform processes have been shown to improve outcomes.  The lessons learned from recent and dramatic stories of implementation of various aspects of a comprehensive safety program on the obstetrical unit demonstrate that such uniform processes have, like in other complex organizations, led to widespread improvement in such outcomes as lowering cesarean section rates and decreasing malpractice claims and costs.10-15  In health care, standardization generally reduces costs.

When considering impediments, two issues quickly took the lead: Miscommunication and normalization of deviance.

Are miscommunication and normalization of deviance challenges that your labor & delivery unit face?  What has your team done to combat them?

Continue reading via Apple Store download or as a PDF

23 Feb

What Regulates Fetal Heart Rate

The following excerpt summarizing the factors regulating the fetal heart rate will be summarized in the free March 16th lunchtime L&D staff training webinar titled “The Physiology of EFM” featuring Emily Hamilton, MDCM.

Register Today

What Regulates the Fetal Heart Rate?

The heart is a muscle with its own pacemaker, conducting system, numerous types of receptors (alpha and beta adrenergic) and direct neuronal connections to both the sympathetic and parasympathetic systems.

The overarching mission of the cardiovascular system is to deliver sufficient oxygen to key organs. Heart rate is an important determinant of this mission.

Ultimately, any influence on heart rate is mediated by one or more of these structures. The basic anatomy and physiology of heart rate control are described in physiology textbooks. In the simple schematic diagram shown in Figure 1, factors which increase heart rate are shown on the left and factors which decrease heart rate are on the right. While this summary provides the basics for understanding heart rate regulation, it is important to remember that our understanding of this physiology continues to evolve.

fetal heart rate physiology

The cardioregulatory center in the medulla oblongata contains an acceleratory center and an inhibitory center. The cardioregulatory center receives input from the central nervous system, reflex pathways and circulating catecholamines. An example of central nervous system influence on the acceleratory response is seen with vibroacoustic stimulation. In response to sudden auditory stimulation, the central nervous system activates the cardioacceleratory center. The cardioacceleratory center increases heart rate directly via sympathetic cardiac nerves which interact with the sinoatrial node to increase the heart rate.

The rapidity of heart rate change is determined by the conditions that trigger the change.

The cardioinhibitory center slows the heart rate via the parasympathetic vagus nerve which can slow heart rate by modulation at various levels, including the sinoatrial node. Reducing cardioinhibitory activity increases heart rate.

Arterial baroreceptors, located in the aortic arch and carotid arteries, are sensitive to stretch or distension of a vessel caused by blood pressure changes. An increase in arterial blood pressure produces vessel distension and causes arterial baroreceptors to send neuronal messages to the cardioinhibitory center, which in turn causes rapid slowing of the fetal heart rate via the parasympathetic vagus nerve. A decrease in arterial pressure results in an increased heart rate.

Arterial chemoreceptors located in the aortic arch and carotid arteries are sensitive to low pH and low oxygen saturation. When these chemoreceptors are activated, they cause the cardioacceleratory center to increase sympathetic impulses, resulting in an increase in the fetal heart rate. The α-adrenergic component of the chemoreceptor response causes vasoconstriction and hypertension. As will be described later, hypertension is an important part of the pathway producing fetal heart rate decelerations.

The catecholamines, epinephrine and norepinephrine, secreted from the adrenal, are both hormones and neurotransmitters. Norepinephrine binds to beta receptors in the heart causing an increase in heart rate, contractility and stroke volume. Catecholamines can also cause redistribution of blood flow by inducing vasoconstriction and vasodilation in different regions. Vasoconstriction is mediated through the α-adrenergic receptors in liver, kidney, skin and gut, and vasodilation is mediated through β adrenergic receptors in skeletal muscle. Catecholamine release is stimulated by the sympathetic nervous system and may be precipitated by stress conditions, such as loud sounds, fear or low blood sugar.

The rapidity of heart rate change is determined by the conditions that trigger the change. Central stimuli like a sudden loud sound or a quick increase in blood pressure cause rapid heart rate changes mediated by direct neuronal pathways to the sinoatrial node. Although chemoreceptor action on heart rate is also mediated neuronally (by the cardiac nerves), this influence tends to be slow because it is triggered by low pH and oxygen levels which tend to fluctuate slowly. Catecholamine mediated effects are relatively slow reflecting their half-life of 2 to 3 minutes.

While all of the mechanisms described above modulate heart rate, it is important to recall that the overarching mission of the cardiovascular system is to deliver sufficient oxygen to key organs. Heart rate is an important determinant of this mission but only one, along with other cardiovascular compensatory mechanisms, which include redistribution of blood flow and changes in blood pressure, cardiac stroke volume or oxygen carrying capacity and hemoglobin-oxygen dissociation in the blood stream. The medulla oblongata contains the vasomotor center that responds to baroreceptors, chemoreceptors and catecholamines. It also regulates peripheral blood vessel dilation and constriction to help maintain normal blood pressure and distribution of blood to vital organs.