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Biomedical subjects

S Chowdhary

Publications and source records attributed to S Chowdhary.

18 recordsLinked to original sources
PubMed2005

The influence of small fibre muscle mechanoreceptors on the cardiac vagus in humans.

We have previously shown that activation of muscle receptors by passive stretch (PS) increases heart rate (HR) with little change in blood pressure (BP). We proposed that PS selectively inhibits cardiac vagal activity. We attempted to test this by performing PS during experimental alterations in vagal tone. Large decreases in vagal tone were induced using either glycopyrrolate or mild rhythmic exercise. Milder alterations in vagal tone were achieved by altering carotid baroreceptor input: neck pressure (NP) or neck suction (NS). PS of the triceps surae was tested in 14 healthy human volunteers. BP, ECG and respiration were recorded. PS alone caused a significant decrease (P < 0.05) in R-R interval (962 +/- 76 ms at baseline compared to 846 +/- 151 ms with PS), and showed a reduction in HR variability, which was not significant. The decrease in R-R interval with PS was significantly less (P < 0.05, n = 3) following administration of glycopyrrolate (-8.1 +/- 4.5 ms) compared to PS alone (-54 +/- 11 ms), and also with PS during handgrip (+10 +/- 10 ms) compared with PS alone (-74 +/- 15 ms) (P < 0.05, n = 5). Milder reductions in vagal activity (NP) resulted in a small but insignificant further decrease in R-R interval in response to PS (-107 +/- 17 ms compared to PS alone -96 +/- 13 ms, n = 5). Mild increases in vagal activity (NS) during PS resulted in smaller decreases in R-R interval (-39 +/- 5.5 ms) compared to PS alone (-86 +/- 17 ms) (P < 0.05, n = 8). BP was not significantly changed by stretch in any tests. The results indicate that amongst muscle receptors there is a specific group activated by stretch that selectively inhibit cardiac vagal tone to produce tachycardia.

Adult↗
PubMed2004

Cutaneous tuberculosis in Indian children: the importance of screening for involvement of internal organs.

AIMS AND OBJECTIVES: Resurgence of skin tuberculosis especially with drug-resistant strains has been well documented in recent years, but this problem has not received much attention in the paediatric age group. Hence, we carried out the present study to analyse the clinical and therapeutic aspects of cutaneous tuberculosis in children. MATERIALS AND METHODS: A detailed clinical examination, investigations, such as haemogram, serology for HIV, Mantoux test, chest X-ray, cytology, culture and histopathology were carried out in all children. They were treated with antitubercular therapy (WHO regimen), and the clinical response was followed up. RESULTS: Of 142 patients with cutaneous tuberculosis, 68 were children (40 females, 28 males). These children were aged from 9 months to 14 years. The duration of the disease varied from 1 month to 6 years. Family history of tuberculosis was present in 28 (41.2%) of the patients. Scrofuloderma was the most common presentation encountered in 30 (44.1%) patients with preferential involvement of the cervical (56.2%) and inguinal (20%) regions. Fifteen (22.1%) patients had lupus vulgaris, of which the keratotic type was the most common (46.7%), 16 had lichen scrofulosorum, three had tuberculosis verrucosa cutis, and four had more than one type of tuberculosis. Involvement of the lung in 14 (20.6%), bone in seven (10.2%), and both in four (5.9%) was found. Histopathology corroborated the clinical diagnosis in 54 (80.6%), culture was positive in six (8.8%). Fifty (73.5%) patients completed the treatment with an excellent response, no multidrug resistant cases were seen. CONCLUSIONS: Cutaneous tuberculosis in children continues to be an important cause of morbidity, there is a high likelihood of internal involvement, especially in patients with scrofuloderma. A search is required for more sensitive, economic diagnostic tools. Response to treatment at 4 weeks often helps in substantiating the diagnosis of tuberculosis in doubtful cases.

Adolescent↗
PubMed2002

Chronotropic effects of nitric oxide in the denervated human heart.

Nitric oxide synthase is expressed in the sino-atrial node and animal data suggests a direct role for nitric oxide on pacemaker activity. Study of this mechanism in intact humans is complicated by both reflex and direct effects of nitric oxide on cardiac autonomic control. Thus, we have studied the direct effects of nitric oxide on heart rate in human cardiac transplant recipients who possess a denervated donor heart. In nine patients, the chronotropic effects of systemic injection of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) (3 mg kg(-1)) or increasing bolus doses of the nitric oxide donor, sodium nitroprusside (SNP), were studied. Injection of L-NMMA increased mean arterial pressure by 17 +/- 2 mmHg (mean +/- S.E.M.; P < 0.001) and also had a significant negative chronotropic effect, lengthening the R-R interval by 54 +/- 8 ms (P < 0.001). This bradycardia was not reflex in origin since injection of the non-NO-dependent vasoconstrictor, phenylephrine (100 microg) achieved a similar rise in mean arterial pressure (18 +/- 3 mmHg; P < 0.001) but failed to change R-R interval duration (Delta R-R = -3 +/- 4 ms). Furthermore, no change in levels of circulating adrenaline was observed with L-NMMA. Conversely, injection of sodium nitroprusside resulted in a positive chronotropic effect with a dose-dependent shortening of R-R interval duration, peak Delta R-R = -25 +/- 8 ms with 130 microg (P < 0.01). These findings indicate that nitric oxide exerts a tonic, direct, positive chronotropic influence on the denervated human heart. This is consistent with the results of animal experiments showing that nitric oxide exerts a facilitatory influence on pacemaking currents in the sino-atrial node.

Cross-Over Studies↗
PubMed2002

Heart rate variability--a therapeutic target?

Reduced heart rate variability (HRV) is a powerful and independent predictor of an adverse prognosis in patients with heart disease and in the general population. The HRV is largely determined by vagally mediated beat to beat variability, conventionally known as respiratory sinus arrhythmia. Thus, HRV is primarily an indicator of cardiac vagal control. It is still unclear whether the relationship between measures of cardiac vagal control and mortality is causative or mere association. Possible mechanisms by which cardiac vagal activity might beneficially influence prognosis include a decrease in myocardial oxygen demand, a reduction in sympathetic activity and a decreased susceptibility of the ventricular myocardium to lethal arrhythmia. In animals, augmentation of cardiac vagal control by nerve stimulation or by drugs is associated with a reduction in sudden death in susceptible models. In humans a number of drugs which have been shown to reduce mortality and sudden death in large randomised trials can also be demonstrated to increase HRV. As a result of this evidence, it has been suggested that the effect of drugs or other therapeutic manoeuvres on HRV might be used to predict clinical efficacy. The use of HRV as a therapeutic target is discussed in this review.

Adrenergic beta-Antagonists↗
PubMed2002

Cysts of the ejaculatory system--a treatable cause of recurrent epididymo-orchitis in children.

PURPOSE: The commonest causes of acutely painful scrotum are torsion (of appendix of the testis or the testis itself) and epididymo-orchitis. Exploration is the only way to prove the diagnosis and multiple such procedures are performed in patients with recurrent epididymo-orchitis. The purpose of our study was to investigate the cause of recurrent epididymo-orchitis in pre-pubertal children. Four children, aged three years or less, were investigated for recurrent left epididymo-orchitis. All four had cystic dilatation of the ejaculatory duct in the region of the prostatic utriculus, associated in two children with ectopic opening of the vas in the bladder. Initial ultrasound appeared to be normal in all four patients, a retrospective review of the sonographic films, however, revealed a retrovesical cyst in three of them. The diagnosis was established by a combination of urethroscopy with retrograde contrast study via the utriculus and open vasography. All four cases were treated operatively by a transtrigonal approach. The cyst was excised in each case. In one, a vasovasostomy was performed between the left and the normal right vas; in the other three the left vas was anastomosed to the blind end of the contralateral seminal vesicle. All four are symptom-free at one year follow-up. Cysts of the ejaculatory duct are a treatable cause of recurrent epididymo-orchitis. Pre-pubertal children with recurrent epididymo-orchitis and no obvious underlying cause should have a thorough sonographic examination of the retrovesical region for cystic lesions.

Child, Preschool↗
PubMed2001

Application of the Malone antegrade continence enema principle in degenerative leiomyopathy.

An 1-year-old boy with degenerative leiomyopathy (DL) presented with a volvulus of the transverse colon. After derotating the volvulus, we constructed a tube colostomy (TC) from the transverse colon. This TC has been used for the past 2 years by the patient for regular deflation of the colon and antegrade colonic enemas (ACE). We present this as a preliminary report of the use of the Malone ACE procedure in a patient with DL and review the relevant literature.

Child↗
PubMed2001

Nitric oxide and hypertension: not just an endothelium derived relaxing factor!

The importance of endothelial nitric oxide (NO) generation in sustaining a tonic systemic vasodilatation is well established. Inhibiting NO production produces hypertension in animals and in humans and not surprisingly there has been considerable interest in establishing whether deficiencies of endothelial NO pathway activity are implicated in the aetiology of essential hypertension. The results of these investigations have been inconsistent with some suggestion that observed deficiencies of both basal and stimulated endothelial NO generation in hypertensive subjects may be an effect rather than the cause of raised arterial pressure. It is increasingly recognised that neuronal production of NO also influences cardiovascular homeostasis through its action as a neuromodulator within the autonomic nervous system. Overall NO has been shown to have sympatho-inhibitory and vagotonic effects, acting by both central and peripheral mechanisms. Sympathetic overactivity, coupled with the permissive role of a depressed level of baroreflex mediated cardiac vagal control, may play a significant role in the genesis of human hypertension. Early work in hypertensive rats suggests that neuronal NO production is impaired at a number of key central sites concerned with autonomic cardiovascular regulation. This data is consistent with the pattern of autonomic dysfunction observed in human hypertension. The possibility that neuronal rather than endothelial production of NO might play a significant role in the aetiology of essential hypertension is a promising area for future human research.

Autonomic Nervous System↗
PubMed2001

Effects of angiotensin II (AT1) receptor blockade on cardiac vagal control in heart failure.

The objective of the present study was to determine the autonomic effects of angiotensin II (AT(1)) receptor blocker therapy in heart failure. In a randomized double-blind cross-over study, we compared the effects of candesartan and placebo on baroreflex sensitivity and on heart rate variability at rest, during stress and during 24 h monitoring. Acute effects were assessed 4 h after oral candesartan (8 mg) and chronic effects after 4 weeks of treatment (dose titrated to 16 mg daily). The study group comprised 21 patients with heart failure [mean (S.E.M.) ejection fraction 33% (1%)], in the absence of angiotensin-converting enzyme (ACE) inhibitor therapy. We found that acute candesartan was not different from placebo in its effects on blood pressure or mean RR interval. Chronic candesartan significantly reduced blood pressure [placebo, 137 (3)/82 (3) mmHg; candesartan, 121 (4)/75 (2) mmHg; P<0.001; values are mean (S.E.M.)], but had no effect on mean RR interval [placebo, 857 (25) ms; candesartan, 857 (21) ms]. Compared with placebo there were no significant effects of acute or chronic candesartan on heart rate variability in the time domain and no consistent effects in the frequency domain. Baroreflex sensitivity assessed by the phenylephrine bolus method was significantly increased after chronic candesartan [placebo, 3.5 (0.5) ms/mmHg; candesartan, 4.8 (0.7) ms/mmHg; P<0.05], although there were no changes in cross-spectral baroreflex sensitivity. Thus, in contrast with previous results with ACE inhibitors, angiotensin II receptor blockade in heart failure did not increase heart rate variability, and there was no consistent effect on baroreflex sensitivity.

Aged↗
PubMed2000

Renal pathological findings in infective endocarditis.

BACKGROUND: Accounts of renal pathological findings in infective endocarditis are mostly based on studies from many years ago. We reviewed a group of patients with infective endocarditis in the light of modern concepts of renal pathology, including the largest reported series of renal biopsies in this condition. METHODS: Renal tissue was available for retrospective study from 62 patients with confirmed infective endocarditis out of 354 diagnosed with the disease between 1981 and 1998 inclusive. Twenty patients had a renal biopsy and 42 a necropsy. RESULTS: Common renal lesions noted were localized infarcts in 31%, noted only in necropsy material, and acute glomerulonephritis in 26%, noted in biopsy and necropsy material. The commonest type of glomerulonephritis was vasculitic, without deposition of immunoproteins in glomeruli. Of the renal infarcts over half were due to septic emboli, mostly in patients infected with Staphylococcus aureus. Acute interstitial nephritis was found in 10% but was more common in biopsy material and seemed attributable to antibiotics. Renal cortical necrosis found in 10% was apparent only at necropsy. There were various other findings in the kidney. CONCLUSIONS: The kidneys are commonly affected in infective endocarditis by a variety of complications of clinical significance. The commonest type of glomerulonephritis does not appear to be attributable to deposition of immune complexes. A renal biopsy may be helpful in the investigation of renal impairment in a patient with infective endocarditis.

Adult↗
PubMed2000

Nitric oxide and cardiac autonomic control in humans.

Cardiac autonomic control is of prognostic significance in cardiac disease, yet the control mechanisms of this system remain poorly defined. Animal data suggest that nitric oxide (NO) modulates cardiac autonomic control. We investigated the influence of NO on the baroreflex control of heart rate in healthy human subjects. In 26 healthy male volunteers (mean age, 23+/-5 years), we measured heart rate variability and baroreflex sensitivity during inhibition of endogenous NO production with N(G)-monomethyl-L-arginine (L-NMMA) (3 mg/kg per hour) and during exogenous NO donation with sodium nitroprusside (1 to 3 mg/h). Increases from baseline (Delta) in high-frequency (HF) indexes of heart rate variability were smaller with L-NMMA in comparison to an equipressor dose of the control vasoconstrictor phenylephrine (12 to 42 microg/kg per hour): Deltaroot mean square of successive RR interval differences (DeltaRMSSD)=23+/-32 versus 51+/-48 ms (P<0.002); Deltapercentage of successive RR interval differences >50 ms (DeltapNN50)=5+/-15% versus 14+/-12% (P<0.05); and DeltaHF normalized power=-2+/-7 versus 9+/-8 normalized units (P<0.01), respectively. Relative preservation of these indexes was observed during unloading of the baroreflex with sodium nitroprusside compared with a matched fall in blood pressure produced by a control vasodilator, hydralazine (9 to 18 mg/h): DeltaRMSSD=-8+/-8 versus -24+/-15 ms (P<0.001); DeltapNN50=-6+/-11% versus -15+/-19% (P<0.01); DeltaHF normalized power=-7+/-13 versus -13+/-11 normalized units (P<0.05), respectively. The change in cross-spectral alpha-index calculated as the square root of the ratio of RR interval power to systolic spectral power in the HF band (although not alpha-index calculated in the same way for the low-frequency bands or baroreflex sensitivity assessed by the phenylephrine bolus method) was attenuated with L-NMMA compared with phenylephrine (Delta=4+/-8 versus 14+/-15 ms/mm Hg, respectively; P<0.02) and with sodium nitroprusside compared with hydralazine (Delta=-7+/-6 and -9+/-7 ms/mm Hg, respectively; P<0.05). In conclusion, these data demonstrate that NO augments cardiac vagal control in humans.

Adolescent↗
PubMed1999

Role of nitric oxide in the regulation of cardiovascular autonomic control.

Alteration in function of the cardiac autonomic nervous system has proved to be a powerful predictor of cardiac death or serious arrhythmia in patients with cardiac disease, yet little is known about the mechanisms by which this system is regulated. Recent evidence suggests that the gaseous molecule nitric oxide (NO) may act as an important mediator in this pathway. Histochemical staining techniques have identified neuronal populations that contain NO synthase within medullary cardio-regulatory sites and their peripheral autonomic pathways. Drugs that modulate the NO pathway (administered both systemically and into the central nervous system) cause changes in pre- and post-ganglionic sympathetic nerve activity that imply that NO serves to inhibit central sympathetic outflow. There is also evidence that NO may attenuate cardiovascular end-organ responses to sympathetic stimulation. Studies suggest that NO modulates cardiac vagal control, increasing the activity of central vagal motoneurons and, more contentiously, contributing to the bradycardic effects of vagal stimulation. NO also modulates so-called 'indirect' vagal inhibition of sympathetic cardiac responses. Additionally, central attenuation of baroreflex-mediated vagal control has been described. There is relatively little information available on the importance of NO in the regulation of human cardiovascular autonomic control. Further well-controlled studies are required.

Autonomic Nervous System↗
PubMed1989

Internal mammary artery grafts: the shortest route to the coronary arteries.

Inadequate length can limit the use of the internal mammary artery (IMA) for coronary revascularization. By following the shortest route from its origin to the recipient coronary artery, IMA use can be maximized. Seven cadavers were studied to determine that shortest route for the left and right IMAs. The shortest route for the left IMA to the left anterior descending coronary, diagonal, and circumflex coronary arteries was through the pericardium (p less than or equal to 0.01). For the right IMA, the significantly shortest routes were across the anterior heart for the left anterior descending and diagonal arteries, through the right pericardium for the right coronary artery or posterior descending artery, and through the pericardium and transverse sinus for the circumflex artery. Thus, any coronary artery can be reached with an in situ IMA, and the route through the pericardium is markedly shorter to ipsilateral coronary arteries.

Coronary Vessels↗