Transthoracic electrical impedance in cases of high-altitude hypoxia

Prediction of quantitative intrathoracic fluid volume to diagnose pulmonary oedema using LabVIEW

Pulmonary oedema is a life-threatening disease that requires special attention in the area of research and clinical diagnosis. Computer-based techniques are rarely used to quantify the intrathoracic fluid volume (IFV) for diagnostic purposes. This paper discusses a software program developed to detect and diagnose pulmonary oedema using LabVIEW. The software runs on anthropometric dimensions and physiological parameters, mainly transthoracic electrical impedance (TEI). This technique is accurate and faster than existing manual techniques. The LabVIEW software was used to compute the parameters required to quantify IFV. An equation relating per cent control and IFV was obtained. The results of predicted TEI and measured TEI were compared with previously reported data to validate the developed program. It was found that the predicted values of TEI obtained from the computer-based technique were much closer to the measured values of TEI. Six new subjects were enrolled to measure and predict transthoracic impedance and hence to quantify IFV. A similar difference was also observed in the measured and predicted values of TEI for the new subjects.

Serial changes in nasal potential difference and lung electrical impedance tomography at high altitude

Recent work suggests that treatment with inhaled beta(2)-agonists reduces the incidence of high-altitude pulmonary edema in susceptible subjects by increasing respiratory epithelial sodium transport. We estimated respiratory epithelial ion transport by transepithelial nasal potential difference (NPD) measurements in 20 normal male subjects before, during, and after a stay at 3,800 m. NPD hyperpolarized on ascent to 3,800 m (P < 0.05), but the change in potential difference with superperfusion of amiloride or isoprenaline was unaffected. Vital capacity (VC) fell on ascent to 3,800 m (P < 0.05), as did the normalized change in electrical impedance (NCI) measured over the right lung parenchyma (P < 0.05) suggestive of an increase in extravascular lung water. Echo-Doppler-estimated pulmonary artery pressure increases were insufficient to cause clinical pulmonary edema. There was a positive correlation between VC and NCI (R(2) = 0.633) and between NPD and both VC and NCI (R(2) = 0.267 and 0.418). These changes suggest that altered respiratory epithelial ion transport might play a role in the development of subclinical pulmonary edema at high altitude in normal subjects.

Serial changes in spirometry during an ascent to 5,300 m in the Nepalese Himalayas

The aims of the present study were to determine the changes in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and peak expiratory flow (PEF), during an ascent to 5,300 m in the Nepalese Himalayas, and to correlate the changes with arterial oxygen saturation measured by pulse oximetry (SpO2) and symptoms of acute mountain sickness (AMS). Forty-six subjects were studied twice daily during an ascent from 2,800 m (mean barometric pressure 550.6 mmHg) to 5,300 m (mean barometric pressure 404.3 mmHg) during a period of between 10 and 16 days. Measurements of FVC, FEV1, PEF, SpO2, and AMS were recorded. AMS was assessed using a standardized scoring system. FVC fell with altitude, by a mean of 4% from sea level values [95% confidence intervals (CI) 0.9% to 7.4%] at 2,800 m, and 8.6% (95% CI 5.8 to 11.4%) at 5,300 m. FEV1 did not change with increasing altitude. PEF increased with altitude by a mean of 8.9% (95% CI 2.7 to 15.1%) at 2,800 m, and 16% (95% CI 9 to 23%) at 5,300 m. These changes were not significantly related to SpO2 or AMS scores. These results confirm a progressive fall in FVC and increase in PEF with increasing hypobaric hypoxia while FEV1 remains unchanged. The increase in PEF is less than would be predicted from the change in gas density. The fall in FVC may be due to reduced inspiratory force producing a reduction in total lung capacity; subclinical pulmonary edema; an increase in pulmonary blood volume, or changes in airway closure. The absence of a correlation between the spirometric changes and SpO2 or AMS may simply reflect that these measurements of pulmonary function are not sufficiently sensitive indicators of altitude-related disease. Further studies are required to clarify the effects of hypobaric hypoxia on lung volumes and flows in an attempt to obtain a unifying explanation for these changes.

Some aspects of biomedical engineering research in New Delhi

Biomedical engineering has been recognized in India for the last decade. Technological developments have been in areas of importance to the country, with several groups actively involved in the promotion of bioengineering, particularly in New Delhi. A group at the National Physical Laboratory has contributed significantly to the field of ultrasonics as well as to the development of piezoelectric transducers for other biomedical uses. The Centre for Biomedical Engineering of the Indian Institute of Technology and the All India Institute of Medical Sciences is one of the country's leading centres producing outstanding work in areas like instrumentation, rehabilitation, biomaterials, modelling and analysis. Research in technology applied to reproductive physiology (an area especially relevant to India's needs) was initiated at this centre. Research at the School of Environmental Sciences, Jawaharlal Nehru University has elucidated the effects and mechanisms of the action of low-energy electromagnetic radiation and ultrasound on biological systems--in one of the school's projects the use of bone material for ultrasonic transducers and optical detectors was successfully demonstrated. A selected list of publications shows the wide spectrum of research carried out at these institutions.

Effect of digoxin and diuretics on high altitude left ventricular dysfunction

Systolic time intervals, stroke volume, cardiac output and (dZ/dt)/RZ index were serially estimated in 51 normal healthy volunteers at sea level, for ten days after air induction to 3658 m altitude and on return to sea level. The subjects were divided into three groups and were administered a diuretic, beta methyldigoxin and placebo in a double blind protocol. The group on placebo showed an increase in heart rate, reduction in stroke index and cardiac index during high altitude exposure with normalization on return to sea level. A deterioration in left ventricular function as manifested by prolongation of pre-ejection period, increase in PEP/LVET ratio, reduction in (dZ/dt)/RZ index and left ventricular ejection time was also noted at high altitude. The subjects on digoxin maintained normal stroke/cardiac index and did not show any significant changes in the parameters of myocardial function. The diuretic group showed more deterioration in the parameters than the placebo group. No significant side effects were noted. Left ventricular dysfunction and reduction of stroke index at high altitudes may be causually related; digoxin administration may prevent them from occurring.

Monitoring of pulmonary fluid volume and stroke volume by impedance cardiography in patients on hemodialysis

Changes of intrathoracic fludi volume during maintenance therapy with hemodialysis were studied in ten patients with the aid of impedance cardiography. It was found that there was a statistically significant correlation between the decrease in body weight and the increase in basic thoracic impedance in the individual patients, but the values differed considerably from one patient to another. Therefore, comparison of sequential measurements is feasible only in one and the same patient. Out of 16 patients with overhydration undergoing dialysis, the stroke volume could not be determined by impedance cardiographic studies in eight, owing to the abnormal morphology of the dZ/dt curve. Moreover, because the basic thoracic impedance was not constant during treatment, the calculated changes in stroke volume did not appear to be reliable. This has to be taken into account when repeated measurements are made under clinical conditions. In some of the patients, the dZ/dt curve displayed interesting anomalies, probably resulting from hemodynamic alterations. The diagnostic meaning of these features is not yet known.

Changes in transthoracic electrical impedance at high altitude

Mean transthoracic electrical impedance (impedance) which is inversely related to intrathoracic extravascular fluid volume was measured in 121 normal healthy volunteers at sea-level and at 3658 metres altitude. Fifty (group A) reached the high altitude location after an hour's journey in a pressurised aircraft. Twenty-five (group D) underwent slow road ascent including acclimatisation en route. Thirty permanent residents (group B) and 16 temporary residents at high altitude (group C) were also studied. Serial studies in the 30 subjects of group A who developed symptoms of high altidue sickness showed a significant decrease of impedance up to the fourth day of exposure to high altitude which later returned to normal. The 4 volunteers who developed severe symptoms showed the largest drop in impedance. A case of acute pulmonary oedema developing at 4300 metres showed an impedance value of 24-1 ohms on admission. After effective treatment the impedance increased by 11-9 to 36-0 ohms. Twenty asymptomatic subjects of group A and 25 of group D showed a small average increase in impedance values at high altitude. These obstructions suggest that measurement of transthoracic electrical impedance may be a valuable means of detecting incipient high altitude pulmonary oedema.

Changes in transthoracic electrical impedance during submaximal treadmill exercise in patients with ischemic heart disease--A preliminary report

Twenty normal subjects and 32 patients with ischemic heart disease (IHD) were subjected to submaximal treadmill exercise. The mean transthoracic electrical impedance (TEI) was measured with a tetrapolar lead system and the changes were correlated to the extent of ST depression observed on an on-line digital computer. Six subjects of pre-excitation syndrome with "false" ST depression were also studied. The normal subjects did not show a significant change of TEI during exercise. The patients with IHD showed a steady and significant decrease in TEI, correlating with the extent of ST depression. Recovery was slow after the cessation of exercise. The subjects with false ST changes showed no decrease of TEI. The changes were more profound in subjects who developed anginal pain during the test. These findings are attributed to an increase in the thoracic blood volume and pulmonary extravascular water due to transient left ventricular dysfunction in angina.