Biomedical subjects

P Dhawale

Publications and source records attributed to P Dhawale.

3 recordsLinked to original sources

PubMed1996

Myocardial signal response to dipyridamole and dobutamine: demonstration of the BOLD effect using a double-echo gradient-echo sequence.

The purpose of this study was to examine the differential myocardial signal responses due to the blood oxygen level dependent (BOLD) effect in magnetic resonance imaging (MRI) under differing conditions of myocardial oxygen supply and demand. The signal response was measured when myocardial blood flow was increased in excess of oxygen demand or when flow was increased in response to increased myocardial oxygen demand. Normal volunteers were studied using a segmented, interleaved, double-echo, gradient-echo sequence at baseline conditions and during pharmacological stress with either dipyridamole (n = 5) or dobutamine (n = 6). Changes in T2* in the myocardium during stress were calculated. Peak coronary flow velocity was measured at rest and during stress using a breath-hold phase contrast technique. Administration of dipyridamole induced a 124 +/- 27% increase in coronary blood flow which resulted in a 46 +/- 22% increase in T2*, consistent with a decrease in myocardial venous deoxyhemoglobin concentration as myocardial oxygen supply exceeds demand. In contrast, the administration of dobutamine resulted in a 41 +/- 25% increase in coronary blood flow but no significant change in T2* (-5 +/- 19%), consistent with a lack of change in myocardial venous deoxyhemoglobin concentration and balanced oxygen supply and demand. Thus, alterations in the relationship between myocardial oxygen supply and demand appear to be detectable using BOLD MRI.

Adrenergic beta-Agonists↗

PubMed1995

Estimation of hypoxic ventilatory dynamics using pseudorandom inputs.

Using experimental and simulation studies, we assessed the applicability of pseudorandom binary hypoxic stimulation (PRBS) for estimating the dynamic respiratory response to a single breath of hypoxia. In experimental studies on rats we tested whether the transient ventilatory response to hypoxia based on the PRBS technique converges to the measured response to a true single breath of hypoxia. Plethysmographic volume recordings were obtained from 7 urethane anesthetized, bilaterally vagotomized rats while the inspired O2 level was switched pseudorandomly between 21% and 12%. The psuedorandom estimates were comparable to the ensemble averaged responses to 15-40 trials of a single-breath inspiration of 12% O2. Ventilation peaked in 2-3 breaths and the response lasted for 15-20 breaths and was primarily due to a decrease in breath duration. Changes in CO2 concentration in the blood cause an underestimate of the purely hypoxic transient response. In simulation studies we also demonstrated the applicability of this technique to human subjects using a mathematical model of human respiratory control. We conclude that the pseudorandom technique will provide a very good estimate of the ventilatory dynamics to inhalation of a single breath of hypoxic gas in rats and humans.

Animals↗

PubMed1993

Measurement by intracoronary ultrasound of in vivo arterial distensibility within atherosclerotic lesions.

Arterial distensibility is diminished by atherosclerosis. This process has not been well studied in the coronary arteries. The purpose of this study was to assess changes in coronary arterial distensibility in 4 groups of patients. Group I (n = 20) consisted of patients with normal vessels, group II (n = 40) with diseased undilated vessels, group III (n = 15) after successful percutaneous transluminal coronary angioplasty (PTCA), and Group IV (n = 20) after successful directional coronary atherectomy (DCA). Intracoronary ultrasound imaging was used to assess distensibility, plaque morphology and atherosclerotic burden (expressed as the percentage of total vessel cross-sectional area occupied by plaque: percent plaque area). Distensibility was defined as percent change in lumen area in a cardiac cycle. Group I (normal vessels) had a distensibility = 14 +/- 5%, which was significantly greater than that seen in group II (distensibility = 4 +/- 2%, p < 0.001). In undilated vessels, distensibility was related to the degree of atherosclerotic burden (r = 0.75). This relation was curvilinear with a marked decrease in distensibility when percent plaque area exceeded 30%. Distensibility in group III (after PTCA) was higher than in group II (10 +/- 3 vs 4 +/- 2%, p < 0.001) despite a larger plaque burden (percent plaque area of 56 +/- 12 vs 46 +/- 11%, p < 0.005). The distensibility in group IV (after DCA) was also higher than in group II (8 +/- 4 vs 4 +/- 2%, p < 0.001) despite a similar residual percent plaque area (49 +/- 13 vs 46 +/- 11%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗