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Biomedical subjects

J L Robotham

Publications and source records attributed to J L Robotham.

At least 91 records · Page 5Linked to original sources
PubMed1983

Regional left ventricular performance during normal and obstructed spontaneous respiration.

To clarify the effects of respiration on left ventricular (LV) dimensions and shortening, we studied chronically instrumented dogs with endocardial sonomicrometer crystals in the anterior-posterior (AP), septal to lateral (SL), and long axes (LA) following pericardiectomy. Ten anesthetized dogs were examined during spontaneous unobstructed respiration, partial inspiratory obstruction (PIO), and Mueller maneuvers (MM). During unobstructed inspiration, end-diastolic dimensions (EDD) demonstrated a significant increase in the AP and a similar decrease in the SL axis (i.e., noncongruent shape changes). During PIO only the SL EDD diminished significantly, while no significant changes occurred in any EDD during MM. Individual dogs also demonstrated noncongruent shape changes at end systole during inspiration. However, the end-systolic dimensions for the entire group demonstrated a significant increase in one dimension during each inspiratory mode with no significant changes in the other two axes suggesting an increased ventricular volume. Regional shortening declined only in the SL axis during both unobstructed respiration and PIO. Spontaneous sighs with large tidal volumes, yet smaller changes in pleural pressure than during the MM, were associated with marked noncongruent shape changes in both diastole and systole. We conclude that 1) estimates of LV volumes during respiration based on only one or two axes and assuming regional congruent shape changes may be misleading; and 2) lung volume changes can affect LV geometry independently of changes in pleural pressure.

Airway Obstruction↗
PubMed1983

Effects of positive and negative pressure ventilation on cardiac performance.

We have critically reviewed our present understanding of the complex hemodynamic events occurring during spontaneous and mechanical ventilation. It is clear that the physiologic events occurring during normal conditions are present but may be relatively less important under pathophysiologic conditions. Furthermore, since spontaneous ventilation and mechanical ventilation are not simply opposites, evaluation of one ventilatory mode aids in understanding the hemodynamic events in the other. While we have not discussed the hemodynamic events during high frequency oscillation, only with a full understanding of both spontaneous respiration and conventional IPPV can the full implications of this new mode of ventilation be appreciated. It seems a reasonable assumption that in the critically ill patient with cardiopulmonary dysfunction, one mode of ventilation will be optimal and another either less so or even detrimental. Only with an understanding of the hemodynamic effects of respiration can the optimal therapeutic modality be tailored to each patient.

Abdomen↗
PubMed1982

Usual interstitial pneumonitis in infancy. Clinical and pathologic evaluation.

Interstitial lung disease is uncommon in infancy and childhood, and the long-term clinical and pathologic evolution of this entity in infants has not been published previously. We describe an infant with a steroid-sensitive chronic interstitial pneumonitis for which the clinical and histopathologic progression of the disease are presented. A family history of interstitial pneumonitis consistent with an autosomal dominant trait was present, and Pneumocystis carinii were found in the lung biopsy specimen.

Biopsy↗
PubMed1981

Cardiovascular disturbances in chronic respiratory insufficiency.

The mechanical factors by which chronic respiratory insufficiency may influence right and left ventricular performance during both spontaneous and mechanical ventilation are reviewed. During a spontaneous inspiration the right heart distends because of increased inflow and increased pulmonary vascular resistance. This decreases the effective left ventricular compliance, through ventricular interdependence, reducing the gradient for pulmonary venous return. The inspiratory decrease in pleural pressure also effectively increases the impedance to left ventricular ejection. An inspiratory increase in abdominal pressure further increases the left ventricular afterload. These factors combine to impair left ventricular performance. During intermittent positive pressure ventilation, left ventricular stroke volume increases early in inspiration. This increased inspiratory flow cannot be attributed to a phase lag in the right heart output reaching the left heart chambers because, even with a constant pulmonary arterial inflow, aortic flow increases during inspiration. Several factors may act in concert to improve left ventricular performance, despite the adverse effects of intermittent positive pressure ventilation on the right ventricle. These include (1) a decrease in right heart volume, increasing left ventricular compliance and hence the gradient for pulmonary venous return; (2) anterograde emptying of the alveolar capillary bed with lung inflation; (3) the increase in pleural pressure decreasing impedance to left ventricular emptying; and (4) physical compression of the heart by the lungs.

Animals↗
PubMed1981

Baroreceptor output during normal and obstructed breathing and Mueller maneuvers.

Cardiovascular control during asthma and other forms of obstructed breathing has not been extensively investigated. Previous studies in dogs have shown that obstructed breathing or an inspiratory effort against a blocked airway (Mueller maneuver) provoke large oscillations in blood pressure. During the inspiratory phase transmural systolic pressure relative to atmosphere drops initially, but transmural systolic pressure relative to intrathoracic pressure can remain unchanged or even increase. Because the carotid baroreceptors are located in the extrathoracic circulation, whereas the aortic baroreceptors are located in the intrathoracic circulation, and each responds to local transmural arterial pressure, simultaneous baroreceptor output from these two areas was measured in the anesthetized cat during normal and obstructed breathing and during Mueller maneuvers. Both whole-nerve and single-fiber preparations showed a significantly decreased output from the carotid baroreceptors during obstructed inspiratory efforts, whereas aortic baroreceptor output decreased significantly less or not at all. Transmural systolic pressure decreased significantly less in the aorta than in the carotid regions. Further, the aortic baroreceptors were more sensitive to changes in pulse pressure than were the carotid baroreceptors. These results suggest a mechanism for stabilizing the cardiac responses to precipitous falls in blood pressure that occur in obstructed breathing.

Airway Obstruction↗
PubMed1981

Effect of PEEP on left ventricular function in right-heart-bypassed dogs.

Positive-pressure ventilation with positive end-expiratory pressure (PEEP) has been associated with elevation of left ventricular filling pressure for a stable or reduced cardiac output. To exclude the possibility that right ventricular distension due to increased pulmonary vascular resistance decreases left ventricular compliance (ventricular interdependence), we studied the effect of PEEP on left ventricular function in open-chest right-heart-bypassed dogs. A rightward shift of the left ventricular function curve was caused by 15 cmH2O PEEP without a change in the aortic pressure-flow relationship. The pericardial pressure, however, was found to exceed atmospheric pressure on 15 cmH2O even with the chest widely opened. This increase in the pressure surrounding the heart accounted for the increase in left ventricular filling pressure. We postulate, therefore, that the elevation in left ventricular filling pressure found with PEEP is due in part, if not entirely, to mechanical interaction of the heart and lungs by direct compression or pericardial traction.

Animals↗
PubMed1980

A physiologic assessment of segmental bronchial atresia.

A child with congenital atresia of the apical posterior bronchus was followed from birth. The obstructed segment, ventilated through collateral pathways, was documented to be aerated by day 6. At 10 yr of age, the anomalous and adjacent normal segments were resected because of respiratory symptoms. Preoperatively, pulmonary function studies showed a mild obstructive ventilatory defect. Postoperatively, although asymptomatic, the patient's obstruction persisted. Collateral resistance (Rcoll) measured between the atretic and adjacent normal segments of the resected lung was comparable to Rcoll in young adults, but markedly greater than Rcoll for emphysematous lungs. Pathologic examination revealed gross emphysematous changes in the anomalous segment. We conclude that collateral pathways exist early in life and that ventilation of lung distal to congenitally absent airways is slow and may contribute to the development of emphysema; we speculate that this lesion should be resected early in life to permit optimal growth and development of the remaining lung.

Airway Resistance↗
PubMed1980

The effects of positive end-expiratory pressure on right and left ventricular performance.

The cardiovascular effects of positive end-expiratory pressure (PEEP) were studied in mechanically ventilated, vagotomized, Beta-blocked, anesthetized dogs. To compensate for the effect of PEEP on decreasing systemic venous return, acute plasma volume expansion was accomplished returning stroke volume and cardiac output to control values. Left and right ventricular filling pressures (LVFP and RVFP) and aortic pressure were measured relative to pressure (transmural pressure). Ventricular performance was assessed by comparing the transmural ventricular filling pressures at similar stroke volumes. Studies were performed on individual dogs with increasing LVFP produced by Beta-blockade, volume expansion, and obstruction of the descending thoracic aorta. Utilizing these methods we observed that for a given cardiac output, transmural LVFP was higher on PEEP compared to a control state with both normal and elevated control LVFP. On the right side, for a given cardiac output, RVFP was elevated only when the control LVFP was elevated. Our results suggest a nonneuronal adverse effect of PEEP on both left and right ventricular performance. This effect is probably due to mechanical heart-lung interaction since left ventricular (LV) dp/dt showed no change.

Animals↗
PubMed1980

The natural history of bronchial atresia. Serial observations of a case from birth to operative correction.

A 10-year-old child presented with a history of intermittent respiratory symptoms since birth. Progressive shift of the mediastinum away from a hyperexpanded left upper lobe to the right side was evident on serial chest films, since birth. Bronchograms demonstrated atresia of the bronchus to the hyperexpanded segment. Xenon washout demonstrated prolonged half-time in the left upper lobe resulting from collateral ventilatory channels. Resection of the apical posterior segment of the left upper lobe was performed without complication. Bronchial atresia with collateral ventilation caused "lobar emphysema" in this patient.

Bronchi↗
PubMed1979

A physiological approach to hemidiaphragm paralysis.

The occurrence of unilateral phrenic nerve injury with the resultant hemidiaphragm paralysis or paresis can cause significant respiratory distress or respiratory failure in infants and children. An early bedside diagnosis of this problem will allow appropriate therapy and prevent needless diagnostic procedures. With the patient in the lateral decubitus position and the paralyzed side up, accentuated paradoxical inspiratory inward epigastric motion ipsilateral to the paralyzed hemidiaphragm can be seen. With the paralyzed hemidiaphragm down, abdominal motion appears to be normal as if the paralyzed hemidiaphragm were plicated. Thus, ventilation may be improved by changing body position as well as instituting ventilatory support while the potential for phrenic nerve recovery is evaluated.

Diaphragm↗