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Biomedical subjects

M J Morton

Publications and source records attributed to M J Morton.

At least 73 records · Page 4Linked to original sources
PubMed1986

Maternal heart rate and stroke volume in the pygmy goat: effects of exercise and cardiac autonomic blockade.

To determine the normal maternal heart rate and stroke volume response to exercise and the role of the autonomic nervous system in this response, pregnant and non-pregnant pygmy goats were studied at rest, during and following treadmill exercise, and after autonomic blockade. Resting heart rates, stroke volumes and cardiac outputs were 10%, 60%, and 76% higher in pregnant compared to non-pregnant animals (P less than 0.05, 0.001, and 0.001 respectively). During exercise, heart rate and stroke volume rose in both pregnant and non-pregnant animals by similar amounts. Immediately post-exercise, stroke volume in pregnant animals dropped precipitously below resting levels by 15% (P less than 0.005) but cardiac output was preserved by heart rate. This fall in stroke volume was not seen in control animals. Autonomic blockade lowered resting and exercise heart rates in both groups without changing stroke volume. The elevations in heart rate and stroke volume in pregnancy are not primarily mediated via the autonomic nervous system. Although the maternal cardiac output response to exercise appears normal, the post-exercise fall in stroke volume, presumed secondary to a reduction in preload, could potentially be harmful to both mother and fetus.

Animals↗
PubMed1986

Filling and arterial pressures as determinants of left ventricular stroke volume in fetal lambs.

Left ventricular (LV) function was investigated in 16 fetal lambs (125-140 days gestation), each instrumented with an electromagnetic flow sensor on the ascending aorta and vascular catheters. Control arterial blood values were pH 7.38 +/- 0.02 (SD), PCO2 46.3 +/- 3.2 Torr, PO2 19.4 +/- 1.3 Torr, and hematocrit 34.8 +/- 4.3%. Control values for LV output (228 +/- 108 ml X min-1 X kg-1) and arterial pressure (AP, 47.4 +/- 6.5 Torr) were unchanged by administration of atropine and propranolol. LV function curves relating stroke volume (SV) to mean left atrial pressure (LAP) were generated by rapid withdrawal and reinfusion of fetal blood with or without concomitant infusion of nitroprusside (NP) or phenylephrine hydrochloride (PE) to lower or raise mean arterial pressure (AP). The control LV function curve was composed of a steep ascending limb of 0.39 +/- 0.34 ml X kg-1 X Torr-1 and a plateau of 0.04 +/- 0.04 ml X kg-1 X Torr-1. The breakpoint joining the limbs of the control curve was LAP 3.1 +/- 1.2 Torr and LVSV 1.3 +/- 0.5 ml/kg, and these values were not different from control LAP and SV. Function curve slopes were not affected by PE or NP treatment. Multiple linear regression of SV, LAP, and AP showed a small but significant coefficient for AP [-0.002 +/- 0.001 (SE) ml X kg-1 X Torr-1] and LAP [+0.053 +/- 0.004 (SE) ml X kg-1 X Torr-1] at LAP greater than breakpoint.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Estradiol and hemodynamics during ovulation induction.

Left ventricular size and stroke volume increase in human pregnancy and during estrogen administration in laboratory animals. In order to determine if elevated levels of endogenous estrogens in humans produce hemodynamic changes similar to those that occur during pregnancy, 14 patients were studied during ovulation induction at day 8 +/- 2 (SD) (proliferative phase) and at day 14 +/- 4 (midcycle) of their cycles. M-mode echocardiography was carried out with the patient in the left lateral decubitus, head down and head up positions. The mean serum estradiol level was 294 +/- 234 (SD) pg ml-1 at day 8 +/- 2 (treatment day) and it increased to 1503 +/- 531 pg ml-1 at day 14 +/- 4 (cycle day) of the same cycle. This change in serum estradiol was significant (P less than 0.001), associated with an increase in left ventricle diastolic dimension of 2.3 +/- 1.1 mm (P less than 0.001). During the same time period stroke volume and cardiac index correspondingly increased. Heart rate, fractional shortening, and blood pressure did not change and systemic vascular resistance decreased. Many of the cardiovascular adaptations of pregnancy are duplicated by high levels of endogenous estrogens and these changes are evident in as few as 6 days. Thus, we conclude that changes in endogenous estrogen correlate with certain cardiovascular parameters, the most striking of which is the left ventricular size. This may be one of the adaptive mechanisms by which the maternal circulation adapts to pregnancy.

Adult↗
PubMed1986

Right ventricular function in the hypoxaemic fetal sheep.

Right ventricular function was investigated in seven fetal sheep (125-130 days gestation) hypoxaemic at a mean of 5 days postoperation, and were compared to nine normoxaemic fetal sheep of the same gestation. Arterial O2 and CO2 tensions, pH, and haematocrit values for the hypoxaemic and normoxaemic fetuses were 15.6 +/- 1.0 vs. 20.6 +/- 1.8 torr, 49.4 +/- 4.1 vs. 46.1 +/- 1.6 torr, 7.38 +/- 0.02 vs. 7.39 +/- 0.02, and 29 +/- 7.5 vs. 31 +/- 5.3%, respectively. Right ventricular output and stroke volume were similar in the two groups, 241 +/- 57 vs. 247 +/- 75 ml X min-1 X kg-1 and 1.5 +/- 0.4 vs. 1.5 +/- 0.4 ml X kg-1, respectively. Filling and afterload pressures were also similar in the hypoxaemic and normoxaemic fetuses with right atrial pressure of 3.0 +/- 1.0 vs. 3.7 +/- 1.2 mmHg, and arterial pressure of 42 +/- 5 vs. 43 +/- 4 mmHg, respectively. Ventricular function curves were produced by rapid withdrawal and re-infusion of fetal blood producing curves with a steep ascending limb and a plateau phase. The breakpoint joining the limbs of the control function curve for the hypoxaemic and normoxaemic fetuses were right atrial pressure 2.9 +/- 1.0 vs. 3.4 +/- 1.2 mmHg and a stroke volume of 1.5 +/- 0.5 vs. 1.5 +/- 0.4 ml X kg-1, respectively. Linear regression of stroke volume against arterial pressure from 30-90 mmHg during infusions of nitroprusside and phenylephrine at right atrial filling pressures greater than breakpoint was stroke volume = 0.018 ml X kg-1 X mmHg-1 arterial pressure +/- 2.25 ml X kg-1. This equation is not different from that calculated in normoxaemic fetuses, and demonstrates that the fetal right ventricle is quite sensitive to changes in arterial pressure. These data indicate that reduction in fetal oxygen content by an estimated 40% does not affect fetal right ventricular function.

Animals↗
PubMed1985

Maternal cardiovascular adaptations to twin pregnancy.

Multiple pregnancy places increased demands on the maternal circulation. Maternal left ventricular size and performance were measured with M-mode echocardiography in women with twin pregnancy in the second and third trimesters, and the findings were compared to those in normal singleton pregnancies. As expected, cardiac output was greater during twin than during singleton pregnancy; however, end-diastolic ventricular dimension was not. Output was increased in twin pregnancy during the second and third trimesters by heart rate and also during the third trimester by stroke volume. Increased stroke volume was effected by increased shortening, thus strongly suggesting increased contractility. Increased maternal heart rate and contractility during multiple gestations suggest that cardiovascular reserve is reduced.

Adaptation, Physiological↗
PubMed1985

Exercise dynamics in late gestation: effects of physical training.

Heart rate and stroke volume were measured serially in subjects at rest in the sitting position and at the onset and end of a 6-minute period of upright bicycle exercise. Twenty-three subjects with normal pregnancy were studied in late gestation and again post partum. Rest and exercise cardiac outputs in late gestation were not different from those in the postpartum period. Heart rate was higher at rest and stroke volume lower during exercise in late gestation than post partum. At the end of exercise, stroke volume fell dramatically in late gestation but not post partum. Ten women prospectively identified as physically fit had responses that were not different from those of the nonfit cohort in late gestation. Post partum, the physically fit women had exercise responses typical of trained persons and different from those of the nonfit cohort. In late gestation, rest and exercise hemodynamics in subjects in the sitting position appeared to be dominated by factors influencing venous return, independent of physical fitness.

Birth Weight↗
PubMed1985

Exercise during pregnancy.

Theoretical arguments suggest that cardiovascular fitness would be desirable during pregnancy but that high-intensity exercise should be avoided; both notions require rigorous testing. Moderate exercise, by normal women with uncomplicated pregnancy, does not appear to affect fetal health. Coexisting maternal medical or obstetrical complications may contraindicate exercise.

Animals↗
PubMed1985

Flow through the foramen ovale of the fetal and new-born lamb.

Right and left atrial pressures were measured in eight chronically instrumented fetal and neonatal lambs. Flows were measured with a combination of electromagnetic flow sensor and microsphere techniques. Three of the fetuses were ventilated in utero during the measurements. Four fetuses were studied as neonates immediately after spontaneous term delivery and one was studied as a normal fetus in utero. Data from these preparations were augmented with seven sets of previously reported data from normal fetuses in utero for analysis. Linear least-squares regression analysis demonstrated that inferior caval vein flow into the right atrium was inversely related to right atrial pressure. This flow could not be demonstrated to depend on the velocity of blood in the inferior caval vein. Non-linear least-squares regression analysis of foramen ovale flow as a function of a power of the flow in the inferior caval vein revealed that the square of the velocity of blood in the inferior caval vein predicted foramen ovale flow. Of the two forces that determine foramen ovale flow in the fetus, pressure difference and kinetic energy, the latter was far larger than the former. These results support the theory that the fetal foramen ovale is maintained in an open position by the kinetic energy of the blood in the inferior caval vein.

Animals↗
PubMed1985

Hemodynamics during pregnancy and sex steroid administration in guinea pigs.

We investigated the time course and possible mechanisms by which the maternal cardiovascular system adapts to the demands of pregnancy. Control, 20-, 40-, and 60-day gestation guinea pigs (total 68 days) and nonpregnant virgin female guinea pigs chronically dosed with cholesterol (control), estrogen (17beta-estradiol), progesterone, and estrogen plus progesterone were studied. In vivo heart rates, pressures, cardiac outputs, blood volumes, and in vitro left ventricular pressure-volume relations were measured. There was no difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, or left ventricular weights between the various pregnant animals or hormone-dosed animals and their respective controls. By 20 days gestation blood volume (24%, P less than 0.005), cardiac output (22%, P less than 0.005), and stroke volume (22%, P less than 0.05) were increased, whereas uterine blood flow was unchanged. Chronic estrogen administration resulted in similar increases in cardiac output (24%, P less than 0.05), stroke volume (31%, P less than 0.05), and blood volume (13%, P less than 0.05). In vitro left ventricular pressure-volume relations were shifted to the right in all pregnant and hormone-dosed groups. Increases in left ventricular size and output occur before changes in uterine blood flow in guinea pig pregnancy, and these adaptations can be elicited by chronic sex steroid administration.

Animals↗
PubMed1984

Cardiac size and function in pregnancy-induced hypertension.

The physiologic cardiac enlargement characteristic of normal pregnancy could result in important left ventricular dysfunction in the presence of elevated blood pressure. Using M-mode echocardiography, we measured left ventricular dimensions, fractional shortening, and radius-to-wall thickness ratio in 23 patients who had a diagnosis of pregnancy-induced hypertension at rest and during isometric exercise. Seventeen subjects with normal pregnancies were similarly studied and served as controls. The average gestation of patients with pregnancy-induced hypertension was 38 +/- 2 weeks, and that of control subjects was 37 +/- 1 weeks. The average age was 25 +/- 5 years for patients with pregnancy-induced hypertension, and that for control subjects was 29 +/- 4 years. The patients with pregnancy-induced hypertension did not show the normal eccentric cardiac enlargement observed during pregnancy; the average radius-to-wall thickness ratio was reduced in patients with pregnancy-induced hypertension. Fractional shortening, a reflection of ventricular performance, was maintained both at rest and during exercise in the hypertensive group. One patient, who did not show a reduced radius-to-wall thickness ratio, had marked reduction of left ventricular performance in the presence of severe pregnancy-induced hypertension. Left ventricular performance in most subjects with pregnancy-induced hypertension is normal. Preservation of left ventricular performance despite increased arterial pressure may be related to the absence of eccentric gestational cardiac enlargement.

Adult↗
PubMed1984

Hemodynamics in the guinea pig after anesthetization with ketamine/xylazine.

The resting hemodynamics were determined in 8 guinea pigs after they were anesthetized with ketamine/xylazine. Measurements were made of blood pressure, heart rate, cardiac output, arterial blood gases, and pH. These measurements were obtained initially at 4 to 5 hours after an injection (IM) of ketamine HCl (25 mg) and xylazine (0.15 mg) was given to anesthetize the animals for catheterization (period 1), again 5 days after the operation (period 2), and finally 4 to 5 hours after a 2nd injection of ketamine/xylazine (period 3). There were no differences in heart rates, respiratory rates, or cardiac outputs among the 3 study periods. However, arterial blood pressure was slightly, but significantly, lowered after, and presumably due to, instrumentation (62 +/- 4 mm of Hg, P less than 0.05) when compared with the 5-day postoperative period (67 +/- 7 mm of Hg) or after the readministration of anesthetics (66 +/- 7 mm of Hg). The partial pressure of carbon dioxide in the arterial blood was slightly lower (4 mm of Hg, P less than 0.05) in both acutely postanesthetic periods (period 1 and period 3) than in the same animals at postoperative day 5 (period 2). This study has demonstrated that resting hemodynamics measured shortly after this anesthesia with ketamine/xylazine are not largely different from those in chronically instrumented animals.

Anesthesia, General↗
PubMed1983

Overestimation of mitral valve gradients obtained by phasic pulmonary capillary wedge pressure.

We investigated the relationship between left atrial (LA) and pulmonary capillary wedge pressure (PCW) in order to define the clinical settings in which PCW may be used to approximate LA pressure and to determine the cause and significance of difference between LA and PCW pressures. Nineteen patients who at cardiac catheterization had LA, PCW, and left ventricular (LV) pressures recorded, had mitral valve gradients and areas determined. Mean PCW and LA pressures correlated well (r = 0.94). Phasic PCW consistently overestimated the MV gradient and underestimated the MV area compared to LA pressure, (8 +/- 4 versus 4 +/- 3 mm Hg, p less than 0.001, 1.3 +/- 0.3 versus 1.6 +/- 0.3 cm2, p less than 0.005, respectively). Three patients had abnormal MV prosthesis function assessed by PCW pressure but not by LA pressure. Diastolic MV gradients between PCW and LV were caused or increased by a slowed y descent in the PCW tracing. Using the PCW pressure may falsely elevate MV gradients and falsely reduce MV areas and lead to incorrect clinical action.

Adult↗
PubMed1983

Progesterone-induced hyperventilation in the guinea pig.

Progesterone-induced hyperventilation has thus far not been reported in animals other than humans. Accordingly we investigated the effects of chronic progesterone treatment on ventilation in guinea pigs. Virgin female guinea pigs were divided into those treated with cholesterol as controls (C), progesterone (P), or estrogen plus progesterone (E&P). All hormones were administered in silastic capsules placed subcutaneously for 28 days. On day 28 arterial blood gases and respiratory rates were determined. Arterial pH was elevated in P- and E&P-treated animals compared with controls (7.43 +/- 0.04 and 7.43 +/- 0.03 vs 7.39 +/- 0.05, respectively, P less than 0.05). Arterial PCO2 was reduced in both progesterone-treated groups compared to controls (33.9 +/- 5.8 (P), 33.1 +/- 2.8 (E&P), 38.0 +/- 4.3 (C)), and was correlated with systemic progesterone concentrations in animals receiving E&P (r = -0.85, P less than 0.01) but not in animals receiving P alone (r = -0.07, P = N.S.). Arterial [HCO-3], PO2 and respiratory rates were not different between groups. We conclude that chronic progesterone administration produces hyperventilation in guinea pigs, and that estrogen facilitates this action of progesterone.

Animal Diseases↗
PubMed1983

Filling and arterial pressures as determinants of RV stroke volume in the sheep fetus.

Right ventricular (RV) function was investigated in nine fetal lambs (125-130 days gestation) that were instrumented with pulmonary artery electromagnetic flow sensors and vascular catheters. Control arterial CO2 and O2 tension, pH, and hematocrit values were 46.1 +/- 1.6 (SD) Torr, 20.6 +/- 1.8 Torr, 7.39 +/- 0.02, and 31 +/- 5.3%, respectively. Control values for right ventricular output (247 +/- 75 ml X min-1 X kg-1), stroke volume (SV, 1.5 +/- 0.4 ml X kg-1), right atrial pressure (3.7 +/- 1.2 mmHg), heart rate (166 +/- 18 beats X min-1), and arterial pressure (AP, 43 +/- 4 mmHg) were unchanged by administration of atropine and propranolol. Withdrawal and infusion of fetal blood with or without concomitant infusion of nitroprusside or phenylephrine produced RV function curves at low, normal, and high arterial pressures. All function curves had a steep ascending limb and a plateau. The breakpoint joining the limbs of the control curve was right atrial pressure 3.4 +/- 1.2 mmHg and SV 1.5 +/- 0.4 ml X kg-1. Increased AP shifted the breakpoint downward. Linear regression of SV on AP from 15 to 95 mmHg at right atrial pressure greater than breakpoint was SV = -0.016 ml X kg-1 mmHg-1 X AP + 2.25 ml X kg-1.

Animals↗
PubMed1983

Left ventricular pressure-volume relations shift to the left after long-term loss of pericardial restraint.

The short-term effect of pericardiectomy is to shift the in vivo left ventricular (LV) pressure-volume curve to the right. We studied nine weight-matched pairs of male guinea pigs 28 to 39 days (mean 35) after complete pericardiectomy or sham thoracotomy to determine the long-term effects of pericardiectomy on LV pressure-volume relations. Hemodynamic and in vitro LV pressure-volume data were collected in matched pairs on the same day, 2 to 3 hr after catheter placement and recovery from anesthesia. Cardiac output was measured by the microsphere reference sample method. Postsurgical weight gain was similar in both groups: 823 +/- 6 (mean +/- SD) to 925 +/- 6 g in the pericardiectomy group and 829 +/- 7 to 927 +/- 7 g in the sham thoracotomy group. We found no difference in LV weight: 1.555 +/- 0.145 g in the pericardiectomy group vs 1.564 +/- 0.148 g in the sham thoracotomy group, nor any difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, cardiac outputs, or stroke volumes (p = NS). LV pressure-volume relations, however, were shifted to the left in the pericardiectomy group (p less than .005). At 10 mm Hg, LV volume in the pericardiectomy group (0.85 +/- 0.22 cc) was less than that in the sham thoracotomy group (1.02 +/- 0.15 cc; p less than .025). The LV stress-elastic modulus relationship was not different between groups (p greater than .30). One month after pericardiectomy, LV pressure-volume relations in vitro were shifted to the left without a change in LV weight, LV elastic modulus, or hemodynamics. We speculate that this shift compensates for the lack of pericardial restraint and returns LV volume and hemodynamics to normal in vivo.

Animals↗
PubMed1983

Cardiac stimulation during ritodrine hydrochloride tocolytic therapy.

The effect of ritodrine hydrochloride tocolytic therapy on left ventricular size and performance was studied during pregnancy by M-mode echocardiography. Ritodrine therapy increased heart rate, calculated stroke volume, ejection fraction, and cardiac output. Left ventricular end-diastolic dimension and systemic arterial pressure were unchanged. Left ventricular velocity of circumferential fiber shortening was markedly augmented. Ritodrine, as currently used for tocolytic therapy, has potent inotropic and chronotropic effects on the maternal heart. These effects suggest that ritodrine tocolytic therapy should be used with caution in patients with latent or manifest heart disease.

Adolescent↗
PubMed1982

Use of sodium nitroprusside in complications of gestational hypertension.

Sodium nitroprusside is a potent and ultrafast-acting antihypertensive agent. Limited clinical experience and uncertainty about toxicity have restricted its use in obstetrics. The authors have used nitroprusside concomitantly with hemodynamic monitoring in 4 obstetric patients with severe pregnancy-induced hypertension unresponsive to conventional therapy. The patients with acute congestive heart failure and pulmonary edema responded rapidly and dramatically to nitroprusside. No signs of fetal distress associated with lowering of the arterial pressure were observed, and significant cyanide levels were not detected in a fetal cord blood sample. Nitroprusside should be reserved for refractory hypertensive emergencies in pregnancy. Hemodynamic monitoring is required for adjusting nitroprusside administration and fluid balance. In short-term usage, the authors' experience suggests that maternal and fetal toxicity may not be serious concerns.

Acute Disease↗