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Biomedical subjects

N K Burki

Publications and source records attributed to N K Burki.

At least 37 records · Page 2Linked to original sources
PubMed1987

Dyspnea.

Dyspnea, an unpleasant sensation of difficulty in breathing, is a common accompaniment of cardiopulmonary disease. The underlying mechanisms generating this sensation are not clearly understood. There does not appear to be any one specific site or specific receptor(s) involved in this sensation; however, reflex increase in central respiratory motor "command," as well as activity of the respiratory muscles, appear to be necessary for the genesis of the sensation. Whether there is a direct dyspnogenic effect of changes in chemical drive (increased arterial PCO2 or decreased arterial PO2) is unclear. Several methods to quantify dyspnea for clinical purposes have been described; techniques using exercise as the stimulus and expressing the response on a visual analogue or Borg category scale appear to be clinically applicable. The specific treatment of dyspnea remains in the experimental stage. The direct effects of exercise conditioning are unclear. A number of drugs (mainly central nervous system depressants) have been examined; preliminary work holds promise, but no particular drug can as yet be recommended for routine clinical use.

Dyspnea↗
PubMed1987

Spirometry and flow-volume curves in healthy, normal Pakistanis.

Previous studies have indicated that lung volumes in healthy, normal Pakistani adults are smaller than measurements reported in comparable healthy European populations; in order to confirm these findings and to examine the relationship of maximal expiratory flow rates to lung volumes, we studied 250 non-smoking healthy subjects (116 men and 114 women) between the ages of 18 and 65 years. The population sample was drawn from urban and rural areas of Pakistan, with low levels of air pollution. The results indicate that the forced vital capacity (FVC) and forced expired volume in 1 second (FEV1) were lower in the Pakistani population compared to European populations and North American populations of European descent. These data are in conformity with previous studies; however, in Pakistani men the effects of age on FVC and FEV1 were slight so that, after the fourth decade, the FVC and FEV1 values are very comparable between the European and Pakistani populations. Amongst Pakistani women, on the other hand, FVC and FEV1 remained lower than in their European counterparts throughout adult life. Maximal expiratory flow rates amongst the men did not correlate with age, and these values were very similar to those reported in age-matched European populations. In women, however, there was a significant correlation of maximal flow rates with age and height, and the maximal expiratory flows were decreased compared to European populations. These data indicate that in Pakistani men pulmonary mechanics may be different to their European counterparts, allowing for higher maximal expiratory flows at any given lung volume.

Adolescent↗
PubMed1987

The relationship between exercise-induced asthma and plasma catecholamines.

In asthmatics, exercise (E1) is known to induce bronchoconstriction; a second period of exercise (E2) within 30 to 90 min induces a lesser degree of bronchoconstriction. The reason for the "refractory" bronchoconstrictor response to E2 is unclear. We studied 6 normal subjects (Group 1) and 12 stable asthmatics to examine the possible relationship between the refractory period and sympathoadrenal function. The asthmatics were further divided into 2 groups, based on the absence (Group 2, n = 5) or presence (Group 3) of an exercise-induced bronchoconstrictor response. In each subject/patient, after control measurements of spirometry and venous blood sampling, a standard level of treadmill exercise was performed, and blood and spirometry were obtained at 1, 5, 15, and 25 min after the end of exercise. A second period of treadmill exercise, of the same level and duration, was then performed, and blood sampling and spirometry were repeated at the same time intervals after the end of exercise. There was no significant (p less than 0.1) difference in baseline plasma epinephrine (Ep), or norepinephrine (Np) levels; however, plasma dopamine (Dp) levels were significantly (p less than 0.05) higher in Group 3. In Groups 1 and 2, FEV1 did not change significantly after the first (E1) or second (E2) exercise periods, but there were significant (p less than 0.01) changes in Group 3 (maximal percent changes in FEV1, delta FEV1%, E1 = -14.4%, E2 = -8.8%), and the delta FEV1% after E2 was significantly (p less than 0.01) less than after E1.(ABSTRACT TRUNCATED AT 250 WORDS)

Asthma↗
PubMed1987

Alterations in ventilatory pattern and ratio of dead-space to tidal volume.

The effects of alterations in ventilatory pattern on the simultaneously measured physiologic and anatomic dead-spaces (VDphys and VDan, respectively) and the dead-space to tidal volume ratio (VD-VT) were studied in 17 healthy normal subjects (13 men, four women, ages 21 to 36 years). There were no significant changes in VDan with increases in respiratory frequency (f) or tidal volume (VT). The VDphys increased (mean change +0.153 L, p less than 0.05) with increase in VT (mean increase +0.84 L, p less than 0.01), but did not alter significantly with a twofold increase in f, at control VT. Increase in VT significantly reduced VD/VT (mean change -10.4 percent, p less than 0.05), but increase in f, at control VT, did not significantly alter VD/VT. These results indicate that in normal subjects, increase in VT alters ventilation/perfusion matching in the lungs, whereas an increase in f, at constant VT, has no effect on ventilation/perfusion matching. Increases in VD/VT cannot, therefore, be ascribed to alterations in ventilatory pattern where either VT, or f, or both are increased.

Adult↗
PubMed1986

The dead space to tidal volume ratio in the diagnosis of pulmonary embolism.

In order to assess the value of the measurement of the physiologic dead space (VD) to tidal volume (VT) ratio in pulmonary embolism (PE), a prospective study was performed in hospital inpatients suspected to have PE (n = 110; mean age +/- SD, 52.2 +/- 15.5 yr). In 16 of 29 patients in whom the diagnosis of PE was excluded on the basis of a normal radioisotope perfusion scan and/or normal pulmonary angiogram, VD/VT was less than 40%; in the other 13 patients, a VD/VT greater than 40% was associated with an abnormal spirogram. In all patients in whom PE was angiographically diagnosed (n = 16), VD/VT was greater than 40%. In the remaining 65 patients, a high probability of PE was rarely (6%) associated with a normal VD/VT, whereas in patients with a low probability of PE, 71% had normal VD/VT values. These data indicate that a VD/VT value of less than 40% makes the diagnosis of PE extremely unlikely, whereas VD/VT value greater than 40% in the presence of a normal spirogram is highly suggestive of PE. The diagnostic sensitivity of a VD/VT greater than 0.4 with a normal spirogram as a positive test of PE, and a VD/VT less than 0.4 excluding the diagnosis of PE was 100%, whereas the specificity was 94%; applying Bayesian analysis, the probability of a correct diagnosis of PE using these criteria in a similar population would be 90.5%, and of excluding PE, 96.7%. Thus, as a diagnostic test in PE, VD/VT measurement is comparable, in terms of sensitivity and specificity, to radioisotope lung scanning.

Adult↗
PubMed1985

Detection of added respiratory loads in patients with restrictive lung disease.

In patients with airways obstruction, inspiratory resistive load detection conforms to Weber's law: the higher the background or intrinsic pulmonary resistance, the greater the threshold resistance (the resistance detected 50% of the time, delta R50). In patients with restrictive lung disease, the pulmonary elastance is increased, and the present study was undertaken to assess whether Weber's law applies to elastic load detection in these patients. In 7 patients with restrictive lung disease caused by interstitial fibrosis, there was a significantly decreased total lung capacity compared with that in 6 normal subjects (mean, 63.1 and 101% predicted, respectively; p less than 0.01) and significantly increased total pulmonary elastance (means +/- SD, 14.4 +/- 4.7 and 9.6 +/- 1.8 cmH2O/L, respectively; p less than 0.05). There was no significant difference (p greater than 0.1) between the 2 groups in delta R50; however, the elastic load detection threshold, delta E50, was significantly greater (p less than 0.05) in the patients than in the normal subjects (mean +/- SD, 2.8 +/- 1.3 and 1.4 +/- 0.4 cmH2O/L, respectively). When the detection threshold was adjusted for the background elastance, however, there was no significant difference between the 2 groups (mean +/- SD, 0.21 +/- 0.1 and 0.15 +/- 0.04, respectively; p greater than 0.05). These results confirm that Weber's law is also applicable to the detection of added elastic loads in patients with restrictive lung disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Effects of acute exposure to high altitude on ventilatory drive and respiratory pattern.

To assess changes in ventilatory regulation in terms of central drive and timing, on exposure to high altitude, and the effects of induced hyperoxia at high altitude, six healthy normal lowland subjects (mean age 19.5 +/- 1.64 yr) were studied at low altitude (518 m) and on the first 4 days at high altitude (3,940 m). The progressive increase in resting expired minute ventilation (VE; control mean 9.94 +/- 1.78 to 14.25 +/- 2.67 l/min on day 3, P less than 0.005) on exposure to high altitude was primarily due to a significant increase in respiratory frequency (f; control mean 15.6 +/- 3.5 breaths/min to 23.8 +/- 6.2 breaths/min on day 3, P less than 0.01) with no significant change in tidal volume (VT). The increase in f was due to significant decreases in both inspiratory (TI) and expiratory (TE) time per breath; the ratio of TI to TE increased significantly (control mean 0.40 +/- 0.08 to 0.57 +/- 0.14, P less than 0.025). Mouth occlusion pressure did not change significantly, nor did the ratio of VE to mouth occlusion pressure. The acute induction of hyperoxia for 10 min at high altitude did not significantly alter VE or the ventilatory pattern. These results indicate that acute exposure to high altitude in normal lowlanders causes an increase in VE primarily by an alteration in central breath timing, with no change in respiratory drive. The acute relief of high altitude hypoxia for 10 min has no effect on the increased VE or ventilatory pattern.

Adolescent↗
PubMed1984

Ventilatory effects of doxapram in conscious human subjects.

The ventilatory effects of a bolus intravenous dose of doxapram (0.37 to 0.47 mg/kg) were studied in ten healthy normal subjects. An immediate significant (p less than 0.001) increase in minute ventilation (VE) was due, in equal part, to significant increases in tidal volume (VT) and frequency (f). The inspiratory (TI) and expiratory time (TE) per breath decreased significantly. Mouth occlusion pressure increased significantly, in association with the increase in VT; there was no change in the ratio of VE to mouth occlusion pressure, indicating that respiratory mechanics did not alter. These results indicate that doxapram increases ventilation in conscious, normal man by an increase in inspiratory neuromuscular drive and a change in central breath timing. The ventilatory and mouth occlusion pressure responses to progressive isocapnic hypoxia and progressive hyperoxic hypercapnia were significantly altered by an intravenous infusion of doxapram (1 mg/min) only in the elevations (Y-intercepts) of the slopes of VE and mouth occlusion pressure; the regression coefficients did not change significantly. These results indicate that in conscious normal subjects, doxapram acts on both the peripheral and central respiratory receptors.

Adult↗
PubMed1984

The effect of subcutaneously administered terbutaline on serum potassium in asymptomatic adult asthmatics.

Several recent reports have linked the administration of beta-adrenergic agents to the development of hypokalemia. This led us to study, under controlled conditions, the effects of a subcutaneous injection of 0.25 mg terbutaline sulfate on serum potassium (K+), sodium (Na+), glucose, and insulin in a group of asymptomatic asthmatics. Heart rate (HR), blood pressure (BP), and forced expiratory volume in one second (FEV) were measured as parameters of beta-adrenergic stimulation. Each of 7 subjects was studied on 2 separate mornings after an overnight fast. Measurements were obtained before and at various time intervals after 0.25 mg) of terbutaline sulfate or 0.25 ml of a normal saline solution (placebo) were injected subcutaneously in a double-blind randomized crossover fashion. Terbutaline injection significantly increased HR and FEV and lowered diastolic BP for a period in excess of 3 h, indicating a prolonged beta stimulatory action of the drug. Significant effects on glucose, K+, and insulin were observed as early as 15 min after terbutaline injection; serum glucose and insulin increased and remained elevated for at least 2 h. Serum K+ fell significantly, reached a peak decline of 14% from the control value at 30 min after the injection and remained decreased for a period in excess of after subcutaneous terbutaline injection should be interpreted in the light of these effects of the drug and that terbutaline should be used with caution in patients prone to hypokalemia.

Adult↗
PubMed1984

Ventilatory regulation in eucapnic morbid obesity.

In morbid obesity, there is an increased hindrance to breathing caused by the effects of the increased mass on the chest wall and abdomen; subjects with morbid obesity can maintain eucapnia by increasing inspiratory neuromuscular drive and/or by altering central breath timing. We studied 23 eucapnic, obese subjects (greater than 190% predicted ideal weight), 7 males and 16 females with a mean age of 36.6 +/- 9.2 yr and 18 healthy, normal male subjects. Total lung capacity, functional residual capacity, and total thoracic compliance were significantly (p less than 0.05) reduced in the obese subjects. At rest, minute ventilation was significantly increased because of an increase in respiratory frequency, which in turn was due to a significant decrease in the expiratory time (TE) per breath; the ratio of inspiratory to expiratory time (TI/TE) was thus significantly altered, indicating an alteration in central breath timing. Resting inspiratory neuromuscular drive (as represented by mouth occlusion pressure) was significantly increased in the obese subjects, but tidal volume was not significantly altered. There was an increased ventilatory responsiveness to hypoxia and relatively decreased ventilatory responsiveness to hypercapnia in the obese subjects. These results indicate that morbidly obese subjects maintain eucapnia primarily by an alteration in central breath timing. Although these subjects have decreased responsiveness to CO2, putting them at some risk of developing respiratory failure under conditions of hypercapnic/hypoxic stress, it is possible that this is counteracted by the increased responsiveness to hypoxia.

Adult↗
PubMed1984

Effects of bronchodilation on magnitude estimation of added resistive loads in asthmatic subjects.

The magnitude estimation of 6 added resistive loads (delta R), ranging from 2.7 to 22.5 cmH2O/L/s, was studied in 7 normal and 6 stable asthmatic subjects. Each subject squeezed a handgrip dynamometer to indicate load magnitude. The magnitude estimation of a range of 5 weights, from 0.1 to 1.0 kg, placed on the hand was also assessed by dynamometry and numerical estimation. Airways resistance and spirometry were measured in each group. Metaproterenol, 0.13 mg, was then given by inhalation; after 15 min, the complete study was repeated. There was a significant bronchodilation in the asthmatic subjects, with a subjective decrease in chest "tightness," but no significant change in the normal subjects. In the control state, the perceived magnitude (psi) of delta R could be expressed by the relationship: psi = K. delta R beta, in accordance with Stevens' law. There was no significant difference (p greater than 0.05) in the value of beta between the normal and asthmatic group (0.55 and 0.67, respectively). However, the y-intercept in the control state was significantly greater in the asthmatics; when the perceived magnitude was expressed in terms of the mouth pressure (Pm) during the loaded breath in the control state, i.e., psi = K.Pm beta, there was no significant difference, either in beta or in the y-intercept. These results suggest that psi is related to Pm and is greater for any delta R in asthmatics because Pm is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1984

A simple technique for cold air and exercise challenge to assess bronchial reactivity: the effects of acute coryzal rhinitis on airway reactivity.

The bronchoconstrictor response to exercise which occurs in asthmatics can be enhanced by the simultaneous inhalation of cold air. We describe here a simple technique for the delivery of sub-freezing inspired air during exercise. We have examined airway function at rest and following cold air/exercise challenge in 24 healthy young adults during acute coryzal rhinitis and six weeks later. There were no clinically significant changes in baseline airway function or airway responsiveness to cold air/exercise in association with acute coryzal rhinitis.

Adult↗
PubMed1983

Clinical investigation of abnormalities of ventilatory regulation.

The clinical assessment of disorders of ventilatory regulation is based on an understanding of the physiology of the control of ventilation in man. Apart from clinical examination and standard pulmonary function tests, recent research studies have provided newer tests that can be applied in clinical practice. These consist mainly of studies of the patient at rest, relating arterial blood gas values to minute ventilation and minute ventilation to mouth occlusion pressure. In selected cases, further insight can be gained by the measurement of ventilation and mouth occlusion pressure during progressive hypercapnia or hypoxia. In rare instances, electromyographic studies of the diaphragm and exercise studies may provide additional clinical information. The rational application of these tests to the assessment of ventilatory disorders provides a clearer understanding of the site and type of abnormality and can provide a better guide to therapy.

Carbon Dioxide↗