Biomedical subjects

M Ramanathan

Publications and source records attributed to M Ramanathan.

At least 19 recordsLinked to original sources

PubMed1992

Respiratory muscle blood flow in exercising dogs after pneumonectomy.

In three foxhounds after left pneumonectomy, the relationships of ventilatory work and respiratory muscle (RM) blood flow to ventilation (VE) during steady-state exercise were examined. VE was measured using a specially constructed respiratory mask and a pneumotach; work of breathing was measured by the esophageal balloon technique. Blood flow to RM was measured by the radionuclide-labeled microsphere technique. Lung compliance after pneumonectomy was 55% of that before pneumonectomy; compliance of the thorax was unchanged. O2 uptake (VO2) of RM comprised only 5% of total body VO2 at exercise. At rest, inspiratory muscles received 62% and expiratory muscles 38% of the total O2 delivered to the RM (QO2RM). During exercise, inspiratory muscles received 59% and expiratory muscles 41% of total QO2RM. Blood flow per gram of muscle to the costal diaphragm was significantly higher than that to the crural diaphragm. The diaphragm, parasternals, and posterior cricoarytenoids were the most important inspiratory muscles, and internal intercostals and external obliques were the most important expiratory muscles for exercise. Up to a VE of 120 l/min through one lung, QO2RM constituted only a small fraction of total body VO2 during exercise and maximal vasodilation in the diaphragm was never approached.

Animals↗

PubMed1992

Recruitment of diffusing capacity with exercise in patients after pneumonectomy.

Patients after pneumonectomy are severely limited upon exercise, but impairments in gas exchange are generally mild. One potential explanation of this observation is the existence of functional reserves of diffusing capacity (DLCO), which may be recruited during exercise, predominantly by increasing pulmonary blood flow (Qc). After pneumonectomy, DLCO reserves are recruited even at rest. To investigate if the pattern of recruitment of DLCO is altered and if reserves of DLCO are exhausted during exercise after pneumonectomy, DLCO, lung volume, and cardiac output were measured by the rebreathing method at rest and at multiple levels of steady-state exercise in eight subjects after pneumonectomy and in eight age- and sex-matched nonsmoking normal subjects. In patients after pneumonectomy, the slopes of increase in DLCO [ml.(min.mm Hg)-1.m-2] with respect to QC [ml.min-1.m-2] were normal (0.91 +/- 0.09 x 10(-3) in the pneumonectomy group, 1.16 +/- 0.12 x 10(-3) in the control group, mean +/- SE, p less than 0.05). Thus, the pattern of DLCO recruitment was not significantly affected by pneumonectomy. The ratio of DLCO/Qc fell more rapidly during exercise in patients after pneumonectomy, but the lowest value of the ratio achieved was relatively normal in all except one patient. Declines in arterial O2 saturation at exercise were mild and insufficient to explain the exercise limitation except in the patient whose DLCO/Qc fell below normal. There was no evidence that an upper limit of recruitment was approached. We conclude that the normal ability to recruit DLCO during exercise after pneumonectomy constitutes an important compensatory feature that prevents significant arterial O2 desaturation. In most patients, exercise is limited by a reduced maximal stroke index before reserves of diffusing capacity are exhausted.

Adult↗

PubMed1991

Estimation of diffusion limitation after pneumonectomy from carbon monoxide diffusing capacity.

In three foxhounds, diffusing capacity for carbon monoxide (DLCO) was reduced by 25-30% after left pneumonectomy. Based on previous morphometric data in animals and physiologic data in humans, this reduction should not result in any impairment in gas exchange. However, experimental evidence indicates that diffusion limitation develops during exercise after pneumonectomy. Our objective is to determine whether this diffusion limitation to gas exchange can be predicted from physiologic measurements of DLCO. DLCO measured by the rebreathing technique was translated into diffusing capacity for O2 (DLO2) using an average conversion factor for canids obtained morphometrically (Weibel et al., Respir. Physiol. 54: 173-188, 1983). Arterial O2 saturation (SaO2) at various intensities of steady state exercise was calculated from DLO2 and measured values of O2 consumption, alveolar PO2, hemoglobin and arterial pH, and compared to observed SaO2. After pneumonectomy, SaO2 declined progressively with increasing exercise load. In all dogs, the observed pattern of arterial O2 saturation could be predicted from DLCO measured at similar work loads. The relationship between predicted (Pr) and observed (Ob) SaO2 is: SaO2(Pr) = 22.73 + 0.77SaO2(Ob), r = 0.92. The slope is significantly less than 1.0 (P less than 0.005), indicating that other factors must also contribute to arterial desaturation. We conclude that physiologic measurement of DLCO is a meaningful indicator of diffusion limitation to gas exchange. In the foxhound, a modest reduction in DLCO significantly impairs O2 transport during exercise; but other gas exchange abnormalities, e.g. ventilation perfusion inhomogeneity, must also develop.

Animals↗

PubMed1991

Recruitment of lung diffusing capacity with exercise before and after pneumonectomy in dogs.

Although the left lung constitutes 42% of the total by weight and volume in dogs, carbon monoxide diffusing capacity (DL) after left pneumonectomy in adults falls less than 30% at rest, indicating a significant increase of DL in the remaining lung. DL normally increases during exercise, presumably by recruitment of alveolar capillaries and surface area as lung volume (Vs) and pulmonary blood flow (Qc) increase. We asked whether the increase of DL in the remaining lung after pneumonectomy in adult dogs could be explained by this kind of passive recruitment by the increased volume and Qc in the remaining lung. We measured the relationship between DL and Qc with a rebreathing technique at increasing treadmill loads in adult foxhounds, before and 6 mo after left pneumonectomy, and the relationship between DL and Vs by the same technique under anesthesia as Vs was expanded. DL was reduced by 29.1% at rest and 26.5% with heavy exercise after left pneumonectomy, indicating either recruitment or new growth in the right lung. With the assumption that the right lung normally receives 58% of the Qc and contains 58% of the DL, DL of the right lung increased with Qc in accordance with the following relationships before and after left pneumonectomy: right lung DL (before pneumonectomy) = 6.44 + 2.40(Qc) (r = 0.963) and right lung DL (after pneumonectomy) = 7.51 + 1.75(Qc) (r = 0.958). Only approximately 7% of the increase in DL from rest to peak exercise could be attributed to the increase in Vs during exercise before pneumonectomy and approximately 15% after pneumonectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effect of pneumonectomy on the remaining lung in dogs.

To determine the magnitude of functional compensation after pneumonectomy and whether compensation is related to maturity of the animal at the time of resection, we performed left pneumonectomy in either adult or 10-wk-old beagles. Studies were performed in adults 7-9 mo after surgery and in puppies 18-23 mo after surgery when the dogs reached full maturity. Results were compared with those in age- and sex-matched unoperated controls. Measurements included pressure-volume relationships, pulmonary hemodynamics, rebreathing studies of lung volume, diffusing capacity and its components, lung tissue volume, and pulmonary blood flow. Computerized-tomographic scans were performed in the puppy groups to determine changes in thoracic shape and size. Morphometric analysis of the lungs was performed under light microscopy. There was partial compensation for loss of one lung by functional improvement in the remaining lung. Compensation was greater in those pneumonectomized as puppies than as adults. Volume of the remaining lung was larger than predicted for a given transpulmonary pressure in both groups. Diffusing capacity, pulmonary capillary blood volume, and lung tissue volume were larger than expected for the normal right lung. After pneumonectomy, compliance of the rib cage was greater in puppies than in adults. Weight of the costal diaphragm was reduced in pneumonectomized puppies. Pulmonary hypertension at rest did not develop, and pulmonary vascular reactivity to hypoxia was unchanged after pneumonectomy in both groups. Significant correlations were obtained between physiological and morphometric measurements.

Age Factors↗

PubMed1991

Regional deformation of the canine diaphragm.

To follow regional deformation of the diaphragm in dogs, radiopaque markers were implanted under surgical anesthesia into different anatomic regions of the muscle in triangular arrays (approximately 1 cm to a side). After recovery from surgery, changes in area and shape of the triangles were followed with biplane cinefluorography during quiet breathing and during inspiratory efforts against an occluded airway (Mueller maneuvers). From changes in shape of the triangles during contraction, area changes were decomposed into a major direction and magnitude of shortening (Eg1) and a minor length change (Eg2) perpendicular to Eg1, both expressed as a fraction of initial length at end expiration. With the use of these techniques, systematic differences in regional area change were observed in different parts of the diaphragm during inspiratory efforts at different lung volumes. Regional area always decreased during contraction in the crural and midcostal zones of apposition to the rib cage. Area decreased less and often increased during inspiratory efforts in the costal dome near the central tendon and in the costal region near its rib cage insertion. Differences in regional area change were not due to differences in the Eg1 in different parts of the diaphragm but were a consequence of differences in widening of the muscle along Eg2 perpendicular to the direction of Eg1. As lung volume was passively increased above functional residual capacity, regional area decreased in all parts of the diaphragm except in the costal regions near rib cage insertion, where area increased.

Animals↗

PubMed1991

Unusual hepatic manifestations in typhoid fever.

This paper deals with two patients with typhoid fever in whom hepatic manifestations were the dominant and presenting features of the illness. The ability of typhoid hepatitis to simulate other common infectious diseases in this region is highlighted. It is recommended that typhoid hepatitis should be included in the differential diagnosis of patients presenting with fever and jaundice particularly in the tropics.

Adult↗

PubMed1991

Haemophagocytosis in dengue haemorrhagic fever: a case report.

Virus associated haemophagocytic syndrome (VAHS), a distinct clinico-pathologic entity, is characterised by systemic proliferation of non-neoplastic histotiocytes showing haemophagocytosis resulting in blood cytopaenia. It has been described in relation to several viruses earlier. Here we describe a young girl who developed this reactive process during the course of dengue haemorrhagic fever (DHF).

Adult↗

PubMed1991

Nonmenstrual toxic shock syndrome--a case report.

We present a young lady who satisfied the criteria for the diagnosis of toxic-shock syndrome (TSS). The differential diagnoses of TSS in the local setting are outlined. The pertinent clinical features of TSS and its increasing association with nonmenstruating females are highlighted.

Adult↗

PubMed1990

Hemodynamic changes after pneumonectomy in the exercising foxhound.

Pulmonary arterial pressure is higher during exercise after pneumonectomy than before. Several factors may contribute to the elevation, e.g., loss of vascular bed, overinflation of the remaining lung, and active pulmonary vasoconstriction. We measured hemodynamic changes during graded exercise in conditioned foxhounds and compared pulmonary pressure-flow relationships before and after left pneumonectomy. Pulmonary arterial pressure-flow relationship in the remaining lung is not altered by pneumonectomy, suggesting that the increase in pulmonary vascular resistance post-pneumonectomy is largely the passive consequence of increased pulmonary blood flow to the remaining lung. The potential for chronic hyperinflation of the remaining lung to increase pulmonary resistance after pneumonectomy may have been counterbalanced by a concomitant reduction in lung elastic recoil. Unexpectedly, both mean systemic blood pressure and hematocrit were higher with respect to cardiac output after pneumonectomy. Cardiac output and stroke volume at any given work load were lower after pneumonectomy than before, and heart rate response was unaltered. This pattern of responses suggests that increases in left and right ventricular afterload may have contributed to the reduction in cardiac output.

Animals↗

PubMed1990

Acute renal failure due to multiple bee stings--case reports.

This report deals with a father and his son who developed acute renal failure following multiple bee stings. The renal lesion in these patients appears to be due to rhabdomyolysis caused by the bee venom. The other mechanisms are also discussed. The need for clinicians to be aware of acute renal failure as a complication of bee stings is stressed.

Acute Kidney Injury↗

PubMed1989

Left ventricular coordinate systems.

Three-dimensional kinematics of radiopaque markers in anterior, posterior, septal, and lateral regions of a major equatorial plane were evaluated in anesthetized dogs by biplane fluoroscopy. Stationary coordinate systems measured marker locations recorded during diastole and systole from a contractile origin at the center of contraction at end systole and from a geometric origin at the intersection with the equatorial plane of the ventricular long axis at end diastole. A time-indexed system measured marker locations at end diastole and at end systole, respectively, from the locations of the geometric origin at end diastole and end systole. Compared to the stationary system with the geometric origin, both the stationary system with the contractile origin and the time-indexed system reduced the variability of the radial components of the contractile displacements between ventricular regions. In contrast to the other two systems, the system with the contractile origin reduced circumferential components to values not significantly different from zero. These results indicate that 1) abnormally contracting regions of the ventricle may be located and their size measured by determining the region where the radial component differs from that in the rest of the equatorial plane and 2) rotation in a major equatorial plane of the ventricle is significant, but the influence of rotation can be minimized by referencing ventricular dimensions to a coordinate system with an origin at the center of contraction.

Animals↗

PubMed1989

Sustained maximal ventilation after endurance exercise in athletes.

Although impaired respiratory muscle performance that persists up to 5 min after exercise is stopped has been demonstrated during exhaustive exercise in normal young men, it is not known whether impaired respiratory muscle function follows endurance exercise to exhaustion in highly trained athletes. To study the effects of exercise on sustained maximal voluntary ventilation immediately after exercise, eight elite cross-country skiers performed a 4-min maximal sustained ventilation (MSV) test before and immediately after exhaustive exercise. Subjects were encouraged to maintain maximal ventilation (VE) throughout the MSV test. To encourage greater effort, rapid visual feedback of VE was provided on a computer terminal along with a target VE based on their 12-s maximum voluntary ventilation (MVV). The subjects (7 males, 1 female) were 18.5 +/- 0.9 yr old (mean +/- SD) and exercised for 62.5 +/- 16.7 min at 77 +/- 5% of their maximum oxygen consumption during which average VE was 106.7 +/- 24.2 l/min BTPS. The mean MVV was 196.0 +/- 29.9 l/min or 107% of their age- and height-predicted MVV. Before exercise the MSV was 86% of the MVV or 176.7 +/- 30.5 l/min, whereas after exercise the MSV was 90% of the MVV or 180.3 +/- 28.9 l/min (P = NS). The total volume of gas expired during the 4-min MSV was 706.7 +/- 121.9 liters before and 721.2 +/- 115.5 liters after exercise (P = NS). In this group of athletes, exhaustive exercise produced no deleterious effects on the ability to perform a 4-min MSV test immediately after exercise.

Adolescent↗

PubMed1989

The prevalence of skin manifestations in thyrotoxicosis--a retrospective study.

The presenting features of 236 thyrotoxic patients seen in the thyroid clinic were reviewed. 18.65% of these patterns had one or more dermatological complaints at presentation. There was no specific difference in this group of patients when compared with the general hyperthyroid population with regard to age, race, sex, duration of hyperthyroidism or biochemical indices of thyrotoxicosis. The two major complaints were itching and alopecia. The prevalence of pruritus at 6.4% in our series was identical to that of other workers, but we had a much lower occurrence of alopecia at 2.6%. The diagnosis of thyrotoxicosis was delayed in two patients in whom the only major complaint was pruritus. These symptoms cleared quickly when these patients became euthyroid. However there were other patients who noted hair loss with anti-thyroid medications. The incidence of vitiligo, eczema, onycholysis in our series was much lower those quoted in the Western literature The occurrence of pretibial myoxoedema in our series is similar to that of other workers from this region. The other miscellaneous manifestations include urticaria, xanthelasma and systemic lupus erythematosis. In conclusion we feel the cutaneous manifestations of hyperthyroidism are common in our patients.

Humans↗

PubMed1989

Adult Still's disease: a missed diagnosis.

Adult Still's disease is now a well recognised distinct clinical entity. Two cases of the disorder are presented to illustrate the protean nature of the syndrome. The literature is reviewed with regards to the diagnosis, management and complications of the condition. The need for the physician to be aware of this condition to avoid unnecessary investigations and delay in instituting effective therapy will be stressed.

Adult↗

PubMed1989

Dysphagia as a primary manifestation of thyrotoxicosis: a case report.

This report deals with a middle aged man in whom the presenting symptom of the disorder was dysphagia. The clinical approach to the final diagnosis of thyrotoxic myopathy causing dysphagia is outlined and the pathophysiology of dysphagia then discussed. The need to include thyrotoxicosis in the differential diagnosis of an otherwise unexplained case of dysphagia is stressed.

Deglutition Disorders↗

PubMed1988

Rapid in vivo determinations of instantaneous right ventricular pressure and volume in dogs.

We have developed a method for measuring in vivo canine right ventricular (RV) volume at a frequency of 60 Hz. In six dogs (17-22 kg), under pentobarbital anesthesia, 18 radiopaque markers were surgically implanted in the RV myocardium to maximally represent the RV shell. The xyz-coordinates of the markers were obtained from biplane cineradiographic recordings. RV volume was calculated from the polyhedron created by the markers by decomposing the polyhedron into 24 tetrahedrons, each of whose volumes could be solved from the xyz-coordinates of markers. RV volume was obtained each 16.7 ms, permitting detailed representation if RV volume dynamics. RV end-diastolic volume, end-systolic volume, and ejection fraction averaged 41.3 +/- 10.9, 23.0 +/- 5.8, and 0.44 +/- 0.05 ml, respectively. By simultaneously measuring RV pressure, RV pressure-volume loops were constructed that demonstrated that RV ejection occurred without significant isovolumic contraction, although isovolumic relaxation occurred at end systole. RV systolic elastance was determined in two dogs by imposing four levels of RV afterload. Maximal systolic elastance averaged 4.14 mmHg/ml under control conditions and 9.20 mmHg/ml during dobutamine infusion.

Animals↗

PubMed1988

Ventricular ejection fractions of linear transformation and ellipsoid models.

Eigenvolumes calculated from a linear transformation model were found previously to be linearly related to balloon volumes in excised hearts. The present study analyzed endocardial marker kinematics in intact, contracting left ventricles by biplane cinefluorography. Ejection fractions of the linear transformation model were compared by linear regression analysis with those of an ellipsoidal model, whose ejection fractions had been documented previously in closed and open-chest dog preparations. Data from 10 dogs indicated a correlation coefficient of 0.98 and a regression equation with close similarity to the line of identity. Ejection fractions calculated from the linear transformation model are concluded to be proportional to actual ejection fractions in intact, beating left ventricles.

Algorithms↗