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Biomedical subjects

R D Levy

Publications and source records attributed to R D Levy.

At least 91 records · Page 5Linked to original sources
PubMed1992

Fall in pulmonary vascular resistance in patients awaiting heart transplantation.

BACKGROUND: Raised pulmonary vascular resistance is associated with decreased survival after orthotopic heart transplantation and patients with this risk factor are usually denied transplantation. In a proportion of cases raised pulmonary vascular resistance may fall with time and medical treatment. METHODS: Seven patients with high pulmonary vascular resistance (range 3.9-6.6 Wood units) at initial assessment for cardiac transplantation were restudied by right heart catheterisation after a period of seven to 17 months. RESULTS: In five of the seven patients the pulmonary vascular resistance had fallen, allowing orthotopic heart transplantation to be performed in four. In one patient the resistance was static and in one it had risen. The mean fall in pulmonary vascular resistance for the group was (mean (SD)) 2.6 (2.7) Wood units, p < 0.05. CONCLUSION: Patients who have been denied transplantation on the basis of their raised pulmonary vascular resistance should be reassessed after four to six months if they remain otherwise clinically suitable.

Adult↗
PubMed1992

Induction of sleep apnoea with negative pressure ventilation in patients with chronic obstructive lung disease.

BACKGROUND: Negative pressure ventilation provides intermittent non-invasive ventilatory assistance for patients with advanced chronic obstructive lung disease. Upper airway obstruction during sleep, a reported complication of the technique, may, however, limit its clinical applicability. METHODS: The effects of nocturnal negative pressure ventilation on ventilation and on indices of sleep quality were investigated in five patients with severe chronic obstructive lung disease (mean (SE) FEV1 31% (3%) predicted) who had completed three months of nightly negative pressure ventilation. Subjects underwent overnight polysomnography on consecutive nights, the first night serving as a control and negative pressure ventilation being provided on the second night. Ventilators were adjusted to result in maximum suppression of the peak phasic electromyogram signal from the diaphragm. RESULTS: Negative pressure ventilation resulted in substantial increases in episodes of obstructive apnoea and hypopnoea (mean (SE)/h 59.3 (19.8) v 3.2 (1.3) on control nights). Most obstructive events, however, were associated with under 3% oxygen desaturation, and the lowest recorded values for overnight oxygen saturation were similar on the two study nights. Negative pressure ventilation was also associated with significant increases in the frequencies of movement arousals and changes in sleep stage. CONCLUSIONS: Negative pressure ventilation applied during sleep to patients with advanced chronic obstructive lung disease may result in the development of recurrent episodes of apnoea and hypopnoea as well as altered sleep quality, which could limit its clinical applicability.

Aged↗
PubMed1992

Exertional dyspnea and ventilation in hyperthyroidism.

Dyspnea is recognized to be an important feature in patients with hyperthyroidism at rest and during exercise. However, its etiology is not well-understood. Since dyspnea is thought to be related to the perception of excessive ventilatory effort, we explored the possibility that dyspnea in these patients might be related to an inappropriate ventilatory response to the increased metabolic rate. We studied 11 hyperthyroid patients and 11 age- and sex-matched controls, performing spirometry, lung volumes, mouth pressure measurements, and incremental exercise test. Central drive was estimated by measuring P0.1 and sensation of dyspnea by the Borg scale. We found that hyperthyroid patients (1) have higher ventilation than normal subjects during exercise even when corrected for VCO2 levels; (2) this increased ventilation is secondary to increased central drive which is correlated to the T3ria level (r = 0.85, p less than 0.01); (3) hyperthyroid patients are more dyspneic than controls; and (4) the increased drive can be normalized by beta-blockade. We conclude that the main ventilatory abnormality in hyperthyroid patients is an inappropriate increase in respiratory drive, possibly secondary to increased adrenergic stimulation.

Adult↗
PubMed1991

Increased plasma endothelin-1 in pulmonary hypertension: marker or mediator of disease?

OBJECTIVE: To explore the role of endothelin-1, a potent endothelial-derived vasoconstrictor peptide, in pulmonary hypertension, by measuring its concentration in arterial and venous plasma. DESIGN: A survey, case series study. SETTING: University-affiliated hospitals and outpatient clinics. PATIENTS: Twenty-seven patients with pulmonary hypertension: 7 with primary, and 20 with secondary pulmonary hypertension of various causes. The control groups (n = 16) comprised 8 healthy volunteers and 8 patients with coronary artery disease but without evidence of pulmonary hypertension. MEASUREMENTS AND MAIN RESULTS: Pulmonary artery pressure was markedly increased (94/43 +/- 23/13 mm Hg) in the patients with pulmonary hypertension. Venous plasma immunoreactive endothelin-1, measured by a specific radioimmunoassay, was significantly higher in patients with pulmonary hypertension (3.5 +/- 2.5 pg/mL, P less than 0.001) than in normal subjects (1.45 +/- 0.45 pg/mL), or patients with coronary disease (0.75 +/- 0.64 pg/mL). The arterial-to-venous ratio of immunoreactive endothelin-1 was significantly greater than unity in primary pulmonary hypertension (2.21 +/- 0.72, P = 0.01), whereas the patients with secondary pulmonary hypertension had a mean ratio not different from 1 (0.97 +/- 0.42). In contrast, the mean arterial-to-venous ratios were significantly less than unity in both control groups (0.59 +/- 0.35, and 0.54 +/- 0.64; P less than 0.02, for normal subjects and coronary disease patients, respectively), indicating a possible clearance of endothelin-1 across the healthy lung. CONCLUSIONS: Patient with pulmonary hypertension have substantial alterations in plasma immunoreactive endothelin-1, which may reflect changes in net release or clearance of endothelin-1 by the lung. In patients with primary pulmonary hypertension, the high levels in arterial compared with venous plasma suggest pulmonary production of endothelin-1, which may contribute to elevated pulmonary vascular resistance.

Adult↗
PubMed1991

Desirability of immediate surgical standby for coronary angioplasty.

OBJECTIVE: To assess the value of emergency surgical standby for percutaneous transluminal coronary angioplasty. DESIGN: Retrospective review of the major complications of coronary angioplasty in a regional cardiac centre. SETTING: All angioplasties were performed in the cardiac catheterisation laboratory of Wythenshawe Hospital with surgical standby in an adjoining operating theatre. PATIENTS: 1262 vessels were dilated in 1032 patients (mean age 53 years) between 1984 and 1989. MAIN OUTCOME MEASURES: In-hospital mortality from emergency surgical revascularisation after angioplasty; the rate of myocardial infarction and overall morbidity. RESULTS: Coronary angioplasty achieved primary success in 90% of cases. Thirty eight (3.7%) patients (five women (mean age 55.8) and 33 men (mean age 53.0] were referred for urgent surgical revascularisation--36 direct to operation and two within 24 hours. All patients survived surgery. Five of the 38 had had a previous angioplasty to the same vessel and one had had previous coronary artery grafts. Four of the 38 had an angioplasty for unstable angina. Eighteen had single, 13 double, and seven triple vessel coronary artery disease. The target vessel was the left anterior descending in 25, right coronary artery in nine, circumflex in three, and the left anterior descending and circumflex coronary arteries in one. Five required external cardiac massage on the way to the operating theatre; two of them had a left main stem occlusion. Four internal mammary artery and 60 reversed saphenous vein grafts were implanted (1.6 per patient). Complete revascularisation was achieved in 36 (94.7%) patients. Q wave myocardial infarction occurred in six (15.8%). The final outcome was: none dead, three patients with angina, one late death, one cerebrovascular accident, one late operation for a new left anterior descending lesion, two patients on diuretics with or without an angiotensin converting enzyme inhibitor. One orthotopic transplant was performed in a patient in whom cardiogenic shock developed after the left anterior descending coronary artery became occluded 72 hours after angioplasty. CONCLUSION: There was no surgical mortality and low morbidity among patients for whom immediate surgical cover was requested.

Angioplasty, Balloon, Coronary↗
PubMed1991

Nasal continuous positive airway pressure facilitates respiratory muscle function during sleep in severe chronic obstructive pulmonary disease.

Patients with chronic respiratory insufficiency due to severe chronic obstructive pulmonary disease (COPD) and presumed respiratory muscle fatigue may benefit from therapeutic maneuvers aimed at reducing the magnitude of inspiratory muscle effort. Recent work has demonstrated that continuous positive airway pressure (CPAP) can significantly reduce inspiratory effort and work of breathing in COPD patients with acute respiratory failure. Accordingly it was reasoned that prolonged CPAP administration may similarly reduce the work of breathing in stable COPD patients with chronic respiratory insufficiency, thereby allowing recovery from respiratory muscle fatigue. The purpose of this study was to determine the feasibility of employing nasal CPAP during sleep as a means of implementing this approach to reducing inspiratory muscle effort in such patients. Standard polysomnographic parameters were recorded during nocturnal administration of nasal CPAP in eight stable patients with severe COPD (FEV1 = 26.7 +/- 3.9% of predicted). Esophageal pressure, diaphragmatic (EMGdi) and parasternal intercostal (EMGic) electromyographic activity, arterial oxyhemoglobin saturation (SaO2), and transcutaneous PCO2 (PtcCO2) were also measured. Breathing pattern was determined by respiratory inductive plethysmography. In each patient an optimum level of nasal CPAP could be determined that produced consistent reductions in indices of inspiratory muscle effort without changing tidal volume or breathing frequency. Highly significant reductions in the tidal excursions of esophageal pressure and the pressure-time integral for the inspiratory muscles occurred at the optimum CPAP level in all patients. EMGdi and EMGic were similarly reduced. SaO2 and PtcCO2 were unaffected by CPAP. These results indicate that nasal CPAP can effectively reduce inspiratory muscle effort during sleep in patients with severe COPD.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Obstructive sleep apnea during pregnancy. Therapy and implications for fetal health.

A 32 yr-old woman in her last trimester of pregnancy was found to have severe obstructive sleep apnea (OSA). The overnight polysomnogram demonstrated an apnea plus hypopnea index of 159 events per hour. Apneas were associated with severe oxygen desaturation to 40% during rapid eye movement sleep, maternal bradycardia, and second degree heart block. External cardiotocography showed normal fetal heart rate reactivity to fetal movements, even during the apneas and episodes of oxygen desaturation. Nasal continuous positive airway pressure at a level of 15 cm H2O effectively treated the apneas and desaturation and had no effect on the fetal heart rate. The patient was induced electively during the 39th wk of pregnancy and gave birth to a newborn with growth retardation. Early recognition and treatment of OSA in pregnancy might prevent problems with fetal development.

Adult↗
PubMed1991

Subclinical cardiac dysfunction in sarcoidosis.

Clinically apparent myocardial disease is infrequent in sarcoidosis. However, autopsy data show myocardial involvement in up to 30 percent of patients. Unexplained exertional symptomatology is a common complaint in patients with sarcoidosis. In this study, we investigated whether abnormal cardiac function might limit exercise performance in patients with sarcoidosis without overt cardiac involvement. We studied exercise responses in 35 patients with sarcoidosis and compared them with 28 untrained controls. Seventy-seven percent of the patients were symptomatic. Pulmonary function test results were lower in the group with sarcoidosis than normal controls, but they were within normal range. Only one patient had evidence of ventilatory limitation to exercise. Sixteen (46 percent) patients had abnormally increased heart rates (HRs) at rest prior to exercise testing and/or with exercise. Rapid HRs were confirmed during daily activities by continuous ambulatory electrocardiographic (ECG) monitoring. Left ventricular ejection fraction (LVEF) was measured to determine if systolic dysfunction could account for abnormal HR responses. Of patients with abnormally increased HRs, five had LVEFs less than 50 percent, and eight had normal LVEFs, of whom 75 percent had tachycardia at rest. Retrospective comparison of HR responses and LVEF between patients who did or did not receive corticosteroids revealed no significant differences between groups. We conclude that abnormal HR responses in patients without evident cardiac sarcoidosis are common and exertional symptoms in this population are often associated with chronotropic abnormalities. The exact mechanisms underlying the chronotropic abnormalities are unclear, but they likely include ventricular systolic dysfunction, sinus node dysfunction from granulomatous infiltration, or combinations of the two.

Adult↗
PubMed1990

The haemodynamic response to ST segment changes during coronary arteriography.

Contrast media are known to cause electrocardiographic and haemodynamic changes during coronary arteriography. There is a tendency to proceed with repeated coronary arteriography unless patients develop chest pain, bradycardia or hypotension. We have related the changes in the ST segment to changes in left ventricular end-diastolic pressure, measuring pulmonary arterial diastolic pressure with a transducer tipped catheter. Twenty-five patients were studied, 15 patients with coronary arterial disease, 2 with syndrome X, 3 with coronary arterial spasm (and underlying coronary disease) and 5 normal controls. In control patients, no changes in the ST segment or pulmonary arterial diastolic pressure were recorded. Patients with syndrome X developed ST segment depression in the absence of changes in pulmonary arterial diastolic pressure. Those with coronary arterial spasm and underlying coronary disease developed ST segment depression and a rise in pulmonary arterial diastolic pressure following most injections. In coronary arterial disease, both painful and silent ST segment depression was noted with a rise in pulmonary arterial diastolic pressure. In some instances, a summation effect arose with repeated injections. Major disturbances in the ST segment may occur during coronary arteriography and result in elevation of left ventricular filling pressure.

Angina Pectoris↗
PubMed1990

Aminophylline and human diaphragm strength in vivo.

The transdiaphragmatic pressure (Pdi) twitch response to single shocks from supramaximal bilateral phrenic nerve stimulation was studied before and after acute intravenous infusions of aminophylline [14.9 +/- 3.1 (SD) micrograms/ml] in nine normal subjects. Stimulation was performed with subjects in the sitting position against an occluded airway from end expiration. Baseline gastric pressure and abdominal and rib cage configuration were kept constant. There was no significant difference in peak twitch Pdi from the relaxed diaphragm between control (38.8 +/- 3.3 cmH2O) and aminophylline (40.2 +/- 5.2 cmH2O) experiments. Other twitch characteristics including contraction time, half-relaxation time, and maximum relaxation rate were also unchanged. The Pdi-twitch amplitude at different levels of voluntary Pdi was measured with the twitch occlusion technique, and this relationship was found to be similar under control conditions and after aminophylline. With this technique, maximum Pdi (Pdimax) was calculated as the Pdi at which stimulation would result in no Pdi twitch because all motor units are already maximally activated. No significant change was found in mean calculated Pdimax between control (146.9 +/- 27.0 cmH2O) and aminophylline (149.2 +/- 26.0 cmH2O) experiments. We conclude from this study that the acute administration of aminophylline at therapeutic concentrations does not significantly affect contractility or maximum strength of the normal human diaphragm in vivo.

Adult↗
PubMed1990

Pulmonary denervation in humans. Effects on dyspnea and ventilatory pattern during exercise.

The role of the pulmonary autonomic nerves in the mediation of respiratory sensation is unclear. Pulmonary neurogenic mechanisms may contribute to dyspnea either directly or indirectly via an influence on the pattern of ventilation. Using human heart-lung transplantation as a model of pulmonary denervation, we studied the ventilatory response, respiratory drive (P0.1), and sensation of breathlessness (modified Borg scale) during maximal incremental bicycle exercise. The subjects were four female heart-lung transplant recipients 3 to 9 months post-transplant and 10 age-matched control subjects. The ventilatory response to increasing CO2 output (VCO2) was higher (p less than 0.001) in transplant recipients than in control subjects, such that ventilation at peak exercise was similar in the two groups despite a lower peak VCO2 in transplant recipients. The ratio of tidal volume to inspiratory capacity increased with increasing ventilation in a similar fashion in both groups. Although the respiratory rate increased more quickly in transplant recipients, it was similar at peak ventilation in the two groups. Ventilatory timing and duty cycle at half-peak and peak ventilation were similar in transplant recipients and control subjects. Dyspnea ratings were not different between the two groups at similar levels of ventilation. Dyspnea as a function of P0.1 was also similar in transplant and control groups. These results indicate that pulmonary neurogenic mechanisms play a role in determining the level, but not the pattern, of ventilation during exercise. Furthermore, these pathways do not appear to contribute significantly to the perception of breathlessness in normal humans.

Adult↗
PubMed1990

Ventilatory muscle support in respiratory failure with nasal positive pressure ventilation.

Long-term intermittent mechanical ventilation results in improvements in ventilatory performance and clinical status between ventilation sessions in patients with chronic respiratory failure. The application of intermittent positive pressure ventilation through a nasal mask (NPPV) is a simple, noninvasive method for the provision of chronic intermittent ventilatory support. We investigated the effects of NPPV on inspiratory muscle activity in three normal subjects and nine patients with acute or chronic ventilatory failure due to restrictive (four subjects) or obstructive (five subjects) respiratory disorders. NPPV resulted in reductions of phasic diaphragm electromyogram amplitude to 6.7 +/- 0.7 percent (mean +/- SEM) of values obtained during spontaneous breathing in the normal subjects, 6.4 +/- 3.2 percent in the restrictive group, and 8.3 +/- 5.1 percent in the obstructive group. Simultaneous decreases in activity of accessory respiratory muscles were observed. The reductions in inspiratory muscle activity were confirmed by the finding of positive intrathoracic pressure swings on inspiration in all subjects. With NPPV, oxygen saturation and PCO2 remained stable or improved as compared with values obtained during spontaneous breathing. These results indicate that NPPV can noninvasively provide ventilatory support while reducing inspiratory muscle energy expenditure in acute and chronic respiratory failure of diverse etiology. Long-term assisted ventilation with NPPV may be useful in improving ventilatory performance by resting the inspiratory muscles.

Adult↗
PubMed1990

Cardiac arrhythmias during exercise in severe chronic obstructive pulmonary disease.

We studied the effect of maximal exercise on the prevalence of arrhythmias in 122 subjects with severe COPD. At rest, ten subjects had supraventricular arrhythmias while 13 had unifocal VPB greater than or equal to 6/min or ventricular bigeminy. At peak exercise, six subjects had supraventricular arrhythmias while 24 had VAs. Univariate and multivariate analysis with logistic regression did not show relationships between exercise-related cardiac arrhythmias and the severity of pulmonary disease, oxyhemoglobin desaturation or ECG evidence of chronic lung disease. Exercise-related arrhythmias were significantly associated with the presence of arrhythmias at rest and 87 percent of subjects who had no arrhythmias at rest did not have any during exercise. In patients with COPD, the development of potentially serious arrhythmias during exercise is uncommon without clinically apparent CAD or arrhythmias at rest. However, routine cardiac monitoring during exercise testing should not be abandoned in this population since VAs can occur despite their absence at rest.

Aged↗
PubMed1989

Effect of saline infusion on body temperature and endurance during heavy exercise.

We tested the hypothesis that volume infusion during strenuous exercise, by expanding blood volume, would allow better skin blood flow and better temperature homeostasis and thereby improve endurance time. Nine males exercised to exhaustion at 84.0 +/- 3.14% (SE) of maximum O2 consumption on a cycle ergometer in a double-blind randomized protocol with either no infusion (control) or an infusion of 0.9% NaCl (mean vol 1,280.3 +/- 107.3 ml). Blood samples and expired gases (breath-by-breath), as well as core and skin temperatures, were analyzed. Plasma volume decreased less during exercise with the infusion at 15 min (-13.7 +/- 1.4% control vs. -5.3 +/- 1.7% infusion, P less than 0.05) and at exhaustion (-13.6 +/- 1.2% vs. -1.3 +/- 2.2%, P less than 0.01). The improved fluid homeostasis was associated with a lower core temperature during exercise (39.0 +/- 0.2 degrees C for control and 38.5 +/- 0.2 degrees C for infusion at exhaustion, P less than 0.01) and lower heart rate (194.1 +/- 3.9 beats/min for control and 186.0 +/- 5.1 beats/min for infusion at exhaustion, P less than 0.05). However, endurance time did not differ between control and infusion (21.96 +/- 3.56 and 20.82 +/- 2.63 min, respectively), and neither did [H+], peak O2 uptake, and CO2 production, end-tidal partial pressure of CO2, blood lactate, or blood pressure. In conclusion, saline infusion increases heat dissipation and lowers core temperature during strenuous exercise but does not influence endurance time.

Adolescent↗
PubMed1989

Negative pressure ventilation. Effects on ventilation during sleep in normal subjects.

Negative pressure ventilation (NPV) is used for ventilatory support of patients with respiratory failure due to neuromuscular disorders and thoracic deformities, and to provide ventilatory muscle rest for patients with severe chronic airflow limitation. To determine whether NPV would result in episodes of upper airway obstruction during sleep, we studied five normal subjects on two consecutive nights with the first night serving as a control and NPV being administered on the second night. Ventilators were adjusted so as to reduce the peak phasic diaphragm electromyogram signal by at least 50 percent. All subjects demonstrated an increase in the total number of apneas + hypopneas per hour on NPV control nights. Although differences were not significant, there was a tendency to develop decreased sleep efficiency, sleep fragmentation and altered sleep architecture with NPV. We conclude that nocturnal NPV can induce sleep apneas and impair sleep quality in normal subjects.

Adult↗