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Biomedical subjects

J M Karemaker

Publications and source records attributed to J M Karemaker.

At least 73 records · Page 4Linked to original sources
PubMed1989

Circumstances surrounding aneurysmal subarachnoid hemorrhage.

The circumstances surrounding aneurysmal subarachnoid hemorrhage were investigated in a group of 500 consecutive patients admitted to a neurosurgical center. Subarachnoid hemorrhage occurred during stressful events in 42.8% of the patients, during nonstrenuous activities in 34.4%, and during rest or sleep in 11.8%. The activities or events preceding subarachnoid hemorrhage were not known in the remaining 11.0%. Men were more likely to have suffered their hemorrhage during stressful events than women (54.1% versus 36.6%; p less than 0.00025). Only 30.1% of aneurysms arising from the internal carotid artery ruptured during stressful events compared with 48.1% of aneurysms at other locations (p less than 0.005). Physiological responses to the various activities and events are discussed as they may relate to mechanisms underlying aneurysmal subarachnoid hemorrhage. Two important factors in the precipitation of aneurysmal rupture are increased arterial blood pressure and decreased cerebrospinal fluid pressure around the aneurysm. These factors result in a high transmural pressure and concomitant wall stress. Physical exertion, activities involving the Valsalva maneuver, and emotional strain are associated with an increase in blood pressure and frequently preceded subarachnoid hemorrhage. Fluctuations in cerebrospinal fluid pressure around the aneurysm mainly occur during Valsalva's maneuver and postural changes.

Adolescent↗
PubMed1989

Pitfalls in the assessment of cardiovascular reflexes in patients with sympathetic failure but intact vagal control.

1. Two patients are described who presented with orthostatic hypotension as the main symptom. The diagnosis was sympathetic failure with intact vagal control. 2. Unusual test results were obtained. Assessment of the integrity of the total baroreflex arc by the Valsalva manoeuvre measuring only heart rate changes proved impossible, since the magnitude and time course of the heart rate response were normal notwithstanding the presence of a blood pressure response typical of sympathetic failure. 3. Sustained handgrip, cold pressor test and mental stress test all could induce a rise in blood pressure, despite the presence of sympathetic vasomotor lesions, but only when accompanied by a rise in heart rate. Efferent parasympathetic blockade by atropine, resulting in an increase in heart rate, was also accompanied by a substantial rise in blood pressure. These findings seem to result from a heart rate rise dependent increase in cardiac output unopposed by reflex vasodilatation. 4. In these patients the only baroreflex way to control blood pressure is by varying heart rate. This condition can be evaluated only if blood pressure and heart rate are measured on a beat-by-beat basis.

Adult↗
PubMed1988

Pharmacokinetic-pharmacodynamic modelling of oxprenolol in man using continuous non-invasive blood pressure monitoring.

The relationship between the plasma concentration of oxprenolol and its haemodynamic effects during physical exercise was studied in 6 healthy volunteers, in whom BP and heart rate (HR) were continuously monitored by non-invasive techniques (Fin-A-Press-Tonometer) during repeated three-minute exercise periods for 8 h after treatment. Using the fitted pharmacokinetic curve, the drug effect was related to its plasma concentration using the Emax model. The mean EC50 for the relationship between drug concentration and heart rate during exercise (HRex) was 73.1 ng/ml, and for systolic blood pressure during exercise (SBPex) it was 112.7 ng/ml. Emax was 29.0% for HRex, and 33.2% for SBPex. There were no consistent differences between the parameters for the effects on HRex and SPBex. Thus, using a new, non-invasive technique for continuous measurement of blood pressure, the effect of a beta-adrenoceptor blocking drug on SBPex was described with similar accuracy as its effect on HRex.

Adult↗
PubMed1988

Continuous non-invasive blood pressure monitoring: reliability of Finapres device during the Valsalva manoeuvre.

Because of the inherent risks of intra-arterial blood pressure monitoring a new non-invasive device, Finapres, which measures blood pressure continuously in the finger, was evaluated in 14 hypertensive and one normotensive subject. Brachial intra-arterial and finger pressures were compared during a control period and a subsequent Valsalva manoeuvre. Visually, blood pressures measured by Finapres faithfully reproduced the intra-arterial recordings in all subjects. From each pressure signal beat to beat systolic, diastolic, and mean blood pressure values and their differences were obtained and the time course of the response and its characteristic features were analysed. During the control period the Finapres measurements were lower than intra-arterial systolic, mean, and diastolic pressures (mean(SD) 1(9.6), 9(6.8), and 4(6.1) mmHg respectively). During the response to the Valsalva manoeuvre the brachial-finger pressure differences showed limited deviation from those during the control period; median differences were at most 6 mmHg occurring late during the intrathoracic strain period and 7 mmHg during the post-release blood pressure overshoot. In general, the Finapres device reproduced intra-arterial patterns faithfully. This device appears to offer a reliable alternative to intra-arterial blood pressure monitoring.

Adult↗
PubMed1988

Inflating one's own cuff does not increase self-recorded blood pressure.

To determine whether the muscular activity required to inflate a blood pressure cuff for self-recording influences the blood pressure at the instant of the subsequent measurement, finger blood pressure was recorded continuously during cuff inflation. Ten normotensive and seven untreated hypertensive subjects used their dominant hands to inflate, in 5 s, an occluding cuff on the same arm up to 200 mmHg. Blood pressure in the middle finger of the other arm was measured continuously by the Finapres device. Korotkoff sounds were determined by a microphone in the arm cuff, and the speed of deflation was kept constant by the investigator at 2-3 mmHg/s. Systolic pressure rose at the onset of inflation, with an average peak of 13 +/- 6 (s.d.) and 12 +/- 8 mmHg above baseline in the normotensive and hypertensive subjects, respectively. Five seconds after the onset of deflation both systolic and diastolic pressures in both groups had returned to baseline levels. Thus, self-inflation of a blood pressure cuff allows a valid measurement of blood pressure provided the recommended guidelines are strictly followed.

Adult↗
PubMed1987

Accuracy of auscultatory blood pressure measurement with a long cuff.

Intra-arterial blood pressure was compared with simultaneous auscultatory measurements in 37 subjects with a wide range of blood pressures and arm circumferences; six cuffs of various lengths and widths were used. Nineteen subjects had an arm circumference of 34 cm or more (mean 40 cm) and the other 18 were considered to be non-obese and had a mean arm circumference of 30 cm. With each larger cuff, in terms of bladder surface area, auscultatory blood pressure decreased a few mm relative to intra-arterial pressure both for systolic and for diastolic measurements. Apart from diastolic pressure measured with the two 12 cm wide cuffs (12 X 23 cm, 12 X 30 cm) in the obese group all other auscultatory measurements differed less than 5% from intra-arterial pressure, albeit with considerable variability among the subjects. The differences in error among measurements with the four largest cuffs in the obese group (13 X 30 cm, 14 X 30 cm, 14 X 38 cm, and a conical cuff) were clinically irrelevant, and there was even less to choose among all six cuffs in the non-obese subjects. These results suggest that auscultatory blood pressure may be measured with acceptable accuracy with a single long bladdered cuff both in subjects with large arms and in subjects with normal sized arms.

Adult↗
PubMed1987

Hemodynamic fluctuations and baroreflex sensitivity in humans: a beat-to-beat model.

A beat-to-beat model of the cardiovascular system is developed to study the spontaneous short-term variability in arterial blood pressure (BP) and heart rate (HR) data from humans at rest. The model consists of a set of difference equations representing the following mechanisms: 1) control of HR and peripheral resistance by the baroreflex, 2) Windkessel properties of the systemic arterial tree, 3) contractile properties of the myocardium (Starling's law and restitution), and 4) mechanical effects of respiration on BP. The model is tested by comparing power spectra and cross spectra of simulated data from the model with spectra of actual data from resting subjects. To make spectra from simulated data and from actual data tally, it must be assumed that respiratory sinus arrhythmia at rest is caused by the conversion of respiratory BP variability into HR variability by the fast, vagally mediated baroreflex. The so-called 10-s rhythm in HR and BP appears as a resonance phenomenon due to the delay in the sympathetic control loop of the baroreflex. The simulated response of the model to an imposed increase of BP is shown to correspond with the BP and HR response in patients after administration of a BP-increasing drug, such as phenylephrine. It is concluded that the model correctly describes a number of important features of the cardiovascular system. Mathematical properties of the difference-equation model are discussed.

Blood Pressure↗
PubMed1986

Acute dysautonomia associated with Hodgkin's disease.

A patient is described with acute dysautonomia associated with Hodgkin's disease. Testing of cardiovascular reflex control showed that this patient had a rare manifestation of autonomic cardiovascular neuropathy, namely intact parasympathetic heart rate control in combination with a sympathetic postganglionic lesion affecting the control of the vascular tree.

Adult↗