Early Heart Rate Research Articles

The effects of rilmenidine on tests of autonomic function in humans.

The effects of rilmenidine, a new centrally acting antihypertensive agent, on a number of tests of autonomic function were investigated in six healthy male volunteers. Baroreflex function (delta RR interval [in milliseconds] with each millimeter of mercury change in systolic blood pressure) was determined in response to changes in pressure after injections of phenylephrine and nitroglycerin. Reflex cardiovascular responses to handgrip and standing, as well as during deep breathing and the Valsalva maneuver, were also investigated. Rilmenidine produced a dose-dependent decrease in blood pressure that was not accompanied by an increase in heart rate. Under conditions of low basal sympathetic activity, rilmenidine enhanced parasympathetic tone during the early reflex heart rate changes that occur immediately after standing and during deep breathing, as well as baroreflex heart rate responses to phenylephrine. During a test of sympathetic function, standing blood pressure, and heart rate after 3 minutes, rilmenidine reduced sympathetic tone.

Spectrum of orthostatic disorders: Classification based on an analysis of the short-term circulatory response upon standing

1. In 31 consecutively referred patients (20 females, 11 males) with overt or suspected orthostatic disorders, the changes in blood pressure and heart rate that occur in the first 2 min of standing were analysed. 2. Blood pressure was measured continuously by Finapres. The blood pressure and heart rate responses after 1-2 min of standing (early steady-state response) were used to classify the patients as follows: group I (n = 17, age 42 +/- 17 years), normal early steady-state blood pressure and heart rate responses; group II (n = 5, age 40 +/- 14 years), combination of normal early steady-state blood pressure and postural tachycardia; group III (n = 9, age 51 +/- 14 years), hypotensive orthostatic response with (4/9) or without (5/9) postural tachycardia. We examined whether additional information could be obtained by beat-to-beat analysis of the initial circulatory response (first 30 s). It was quantified by identifying the blood pressure trough and overshoot and the maximum heart rate and relative bradycardia. 3. The initial drop in systolic and diastolic blood pressures did not differ between the three groups. A recovery of blood pressure with a systolic and/or diastolic blood pressure overshoot was present in all group I and II patients, but was absent in all except two patients in group III. The initial maximum heart rate increase did not differ between the three groups. The relative bradycardia was less in groups II and III than in group I. 4. We conclude that analysis of the beat-to-beat blood pressure changes in the first 30 s after the onset of standing provides almost all the information that is necessary to determine abnormalities in orthostatic circulatory control.

Continuous, noninvasive measurement of fetal oxygen and carbon dioxide levels in labor by use of mass spectrometry

Clinical evaluation of the continuous, simultaneous measurement of fetal scalp surface oxygen and carbon dioxide partial pressures by mass spectrometry was undertaken for 52 labors. The mass spectrometer (MM8–80, V.G. Gas Analysis, Winsford, England) was easy to operate and had good long-term stability. The mean drifts for both oxygen and carbon dioxide over the study periods were <2 mm Hg. The mean (±SD) cervical dilatation at the time of transducer application was 6.1 (±1.9) cm and the mean (±SD) duration of the studies was 169 (±122) minutes; 10.5% of the transducer applications were unsuccessful. Falls in fetal scalp surface oxygen levels and rises in carbon dioxide levels were more frequent with late than with variable and with variable than with early fetal heart rate declerations and with increasing severity and frequency of decelerations. Fetal scalp surface pressure changes also occurred with fetal heart rate variability changes, including some related to behavioral state changes. There was not a constant reciprocal relationship between oxygen and carbon dioxide changes, and fetal heart rate patterns were not related to actual blood gas levels. Fetal scalp surface measurements were related to both fetal blood sample and umbilical artery results. Trends in both oxygen and carbon dioxide levels during the course of labor were compared and related to other fetal variables, and most of the time the scalp surface measurements were an accurate guide to systemic blood gas levels. Maternal oxygen administration resulted in significant increase in fetal scalp surface oxygen levels, and on two of eight occasions it also led to decreases in fetal carbon dioxide levels. Scalp surface gas measurement by means of mass spectrometry is a powerful new method of intrapartum fetal monitoring, which should increase the precision of fetal surveillance as well as allow the accurate assessment of both established and new methods for optimizing labor and delivery.

Fetal Response to Cephalopelvic Disproportion

Summary A group of African primigravidae undergoing trial of labour were studied along with a control group to assess the specific fetal responses to the possible excessive head compression encountered in cephalopelvic disproportion (CPD). Depending on the outcome of labour, the patients were placed in one of three groups: major CPD, minor CPD and primary uterine dysfunction with no CPD. Particular attention was directed to the fetal heart pattern evoked and the degree of head moulding produced. In the pbresence of marked CPD, the fetus initially responded with early prolonged fetal heart rate decelerations. These continued and as labour progressed, the late decelerations and falling pH typical of hypoxia developed. The early prolonged dip was a steep deceleration which started early, had no time lag and returned to the base line rate late in relation to the end of the contraction. An objective scoring method described the amount of head moulding present. A score of 6 was considered to represent marked moulding. If the patient was still undelivered after a further two hours of strong contractions with no head descent, then it had become excessive. On its own account, excessive moulding should be regarded as a sign of fetal distress.

Fetal response to cephalopelvic disproportion.

SummaryA group of African primigravidae undergoing trial of labour were studied along with a control group to assess the specific fetal responses to the possible excessive head compression encountered in cephalopelvic disproportion (CPD). Depending on the outcome of labour, the patients were placed in one of three groups: major CPD, minor CPD and primary uterine dysfunction with no CPD. Particular attention was directed to the fetal heart pattern evoked and the degree of head moulding produced. In the pbresence of marked CPD, the fetus initially responded with early prolonged fetal heart rate decelerations. These continued and as labour progressed, the late decelerations and falling pH typical of hypoxia developed. The early prolonged dip was a steep deceleration which started early, had no time lag and returned to the base line rate late in relation to the end of the contraction. An objective scoring method described the amount of head moulding present. A score of 6 was considered to represent marked moulding. If the patient was still undelivered after a further two hours of strong contractions with no head descent, then it had become excessive. On its own account, excessive moulding should be regarded as a sign of fetal distress.

Continuing studies of noise and cardiovascular function

Long term trends in heart rate were observed in a free-moving rhesus monkey. Initially, normal heart rate for the animal was defined over a span of 4 months. She was then exposed to a community noise recording 12 hours per day for 7 weeks. Pre- and post-exposure changes were noted in several aspects of cardiac function. During the exposure period, heart rate and proportion of aberrant EKG responses rose significantly above, then fell significantly below, baseline levels. Patterns of diurnal rhythm for early morning heart rate were also altered by noise exposure. These last results are consistent with those of an earlier study in which a restrained animal was subjected to similar stimulus conditions. The after effects of the single, prolonged noise exposure episode have dissipated gradually. During the course of a 4 month post-exposure period, heart rate and proportion of aberrant EKG responses have slowly returned to near baseline levels. Early morning diurnal rhythm for heart rate has not yet returned to its pre-exposure pattern.

Fetal Distress in the First Stage of Labour Associated with Early Fetal Heart Rate Decelerations and a Short Umbilical Cord

Summary: Five cases of fetal distress early in the first stage of labour associated with a primary short umbilical cord (less than 35 cm) are described. These are used to illustrate the difficulty of correlating changes in fetal heart rate patterns with fetal distress in labour. The importance of fetal blood sampling as the final arbiter in the diagnosis of fetal hypoxia is emphasised.

THE RESPIRATORY AND CARDIOVASCULAR RESPONSE TO IMMERSION IN COLD AND WARM WATER

During their first few minutes of immersion in stirred water at 5 and 15° C. the pulmonary ventilation of twelve unclothed men was high, and their end‐tidal pCO2 fell. The pCO2 then returned to or a little above its original level but did not greatly exceed it even in working experiments lasting 20 min. in water at 5° C. or 40 min. in water at 15° C. Although work reduced or reversed the initial fall in pCO2, these results therefore do not bear out predictions that the pCO2 would rise to dangerous levels during hard work in cold water, at least in immersions of moderate duration.In water at 37·8° C. the men's heart rates rose steadily, in water at 25° C. they fell and remained low, and in water at 5 and 15° C. they rose and then fell. Repeated immersion at 15° C. reduced or abolished the early respiratory and heart rate responses to immersion and the metabolic response, but did not significantly increase the falls in rectal temperature. Clothing also reduced the reflex responses to immersion. A number of ventricular extrasystoles were observed during the first 2 min. of immersion in water at 15° C., and it is suggested that ventricular fibrillation due to increased venous and arterial pressures, adrenaline, and hyperventilation, may be responsible for some cases of sudden death in cold water.