Micro (mi) RNA and Diabetic Retinopathy.

Diabetic Retinopathy (DR), a debilitating microvascular complication of diabetes, is one of the leading cause of blindness. However, the pathogenesis of this disease is not fully understood. Few Studies have reported the role of MicroRNA (miRNA), which is deregulated or altered in many diseases. Further, few pathways linked genes which have been suggested to be regulated by miRNAs, may play an important role in the regulation of glucose homeostasis and eventually may contribute to the establishment of DR. However, the roles of microRNAs (miRNAs) in DR are still not very clear. In current review, we explored various findings of scientific database demonstrating the role of miRNA in the progression and development of Diabetic Retinopathy.

Cardiac Output Assessment by Transthoracic Electrical Bio-impedance in Patients of Acute Myocardial Infarction: Comparative Analysis with Echocardiography.

Objectives: Transthoracic electrical bio-impedance (TEB) has been proposed as a non-invasive and continuous method of cardiac output (CO) measurement, but it still has not found wide usages in clinics. The present study measured CO, using a new instrument NICOMON, and compared it with Echocardiography (ECHO) in acute myocardial infarction (AMI) patients. Methods: In the present study 100 patients of AMI were assessed by both ECHO and NICOMON for cardiac output and ECHO is considered as a reference method for comparison. TEB CO was measured by passing an alternating current and measuring the bio-impedance across the thorax. End diastolic volume (EDV), End systolic volume (ESV) & Left ventricular outflow tract (LVOT) diameter, measured by ECHO were used to calculate CO. Various statistical methods like "t"-test & correlation coefficient (r) were used where found suitable. Results: Results: Mean TEB-CO (4.03±1.11 l/min) was significantly higher (p<0.001) than mean ECHO-CO (3.80±1.28 l/min) with a mean difference of 0.25±1.02 l/min. Conclusions: NICOMON measures CO non-invasively but, it needs more elaborative studies on a larger sample to establish it as an alternative method of ECHO for cardiac output measurement on regular basis.

Role of Vitamin-D in the prevention and treatment of Alzheimer's disease.

Alzheimer's disease is the most common form of age related cognitive impairment. Aim of the present study was to see the effect of vitamin D on cognitive function in elderly. The study was conducted in Department of Physiology, King George's Medical University (KGMU). A total of 80 subjects were enrolled based on Mini Mental State Examination (MMSE) score < 24 and vitamin D deficiency. They were divided into two groups as Group A (case) and Group B (control), each group having 40 subjects. Intervention (Vitamin D supplementation) was given in Group A. The assessment of dementia was done by Mini Mental State Examination (MMSE) score. Every subject was clinically evaluated and estimation of vitamin D was done by direct ELISA kit. Gender, weight, height, BMI, residence and education were also similar between two groups. A significant (p=0.0001) change in MMSE score was observed in both Group A and Group B from baseline to 3 & 6 months and from 3 to 6 months, however, mean change was higher in Group A than Group B. In conclusion, vitamin D supplementation caused significant improvement in the cognitive performance in subjects with senile dementia.

Association of Resistin with Insulin Resistance and Factors of Metabolic Syndrome in North Indians.

Metabolic syndrome (MetS) is a cluster of interrelated common clinical disorders. The role of resistin in insulin sensitivity and MetS is controversial till date. So, the aim of the present study was to investigate the relationship of plasma resistin levels with markers of the MetS in Indian subjects. In a case control study, total 528 subjects were selected for the study. 265 (194 male and 71 female) were cases (with MetS) and 263 (164 male and 99 female) were controls (without MetS). Required anthropometric measurements and calculations were carried out accordingly. All the Biochemical estimations were carried out according to standard protocol. Resistin level was measured by the standard protocol (By ELISA i.e. enzyme linked immunosorbent assay) as illustrated in the kit. Insulin level was also measured by the standard protocol as illustrated in the kit and insulin resistance was calculated by the standard procedures. Plasma resistin levels were significantly higher in cases compared with controls (male = 13.05 ± 4.31 vs. 7.04 ± 2.09 ng/ml; p ≤ 0.001 and female = 13.53 ± 4.14 vs. 7.42 ± 2.30 ng/ml; p ≤ 0.001). Plasma resistin levels were well correlated with waist circumference, glucose, triglycerides, waist/hip ratio, systolic and diastolic blood pressure, high density lipoprotein, total cholesterol, serum low density lipoprotein, serum very low density lipoprotein, insulin and insulin resistance. Plasma resistin levels were elevated in presence of the MetS and were associated with increased metabolic risk factors.

Association of diabetic autonomic neuropathy with red blood cell aldose reductase activity.

OBJECTIVE: Activation of polyol pathway based on increased activity of aldose reductase (AR) has been implicated in the development of diabetic complications including diabetic autonomic neuropathy (DAN). The relationship between DAN and hyperglycemia-induced activation of polyol pathway is still uncertain. In the present study, we investigate the association between aldose reductase activity and diabetic autonomic neuropathy by measuring AR level in red blood cells (RBC). METHOD: In this study, 145 subjects with diabetes with or without DAN and 32 subjects without diabetes have been included. All subjects have been investigated for autonomic function tests and RBC aldose reductase activity. DAN was defined if results of any 2 of the tests of parasympathetic function were abnormal. RBC aldose reductase level was determined spectrophotometrically and expressed as unit/g of hemoglobin. The values were expressed as mean ± standard deviation, and ANOVA test has been applied for comparison between groups. RESULTS: RBC aldose reductase activity was found to be significantly higher in people with diabetes with autonomic neuropathy in comparison to people with diabetes without autonomic neuropathy and healthy individuals without diabetes. Aldose reductase (AR) level ranges from 0.8 units/g Hb to 14.2 units/g Hb. The mean AR level was 8.6±2.95 units in subjects of DM with autonomic neuropathy, while mean AR level was 4.1±1.78 units and 2.0±0.89 units in people with diabetes without neuropathy and normal healthy individuals, respectively (p<0.001). CONCLUSIONS: High aldose reductase activity is associated with the presence of autonomic neuropathy in subjects of type 2 DM.

A study on association of leptin receptor gene polymorphism with obstructive sleep apnea syndrome in overweight and obese north Indian subjects.

Obesity is an important risk factor of Obstructive Sleep Apnea Syndrome (OSAS). Previous studies suggested Leptin Receptor (LEPR) gene Polymorphisms is associated with obesity and OSAS. Study was conducted to asses association of LEPR gene polymorphism K109R, Q223R and K656N with OSAS in North Indian subjects. Genotyping and estimation of serum Leptin levels were done in 190 subjects. Polysomnography, anthropometrical measures and biochemical investigations were done in all the subjects who qualified for inclusion in the study. We observed significant association of Q223R gene polymorphism with blood pressure (BP) (P < 0.05) and nocturnal max pulse rate (P < 0.05). K656N gene polymorphism was associated with AHI (P < 0.05), average desaturation levels (P < 0.05) and HDL-C (P < 0.05). No association was observed in genotype distribution of these subjects according to obesity and disease severity. These findings suggest that LEPR Q223R and K656N gene Polymorphism may influence BP, Max Pulse rate, AHI, Average desaturation levels and HDL levels in these Subjects.

A Case-Control Study Utilizing Red Cell Distribution Width as a Bio-Inflammatory Marker in Pre-eclampsia.

INTRODUCTION: This research was conducted to assess the effectiveness of red cell distribution width (RDW) as an indicator for pre-eclampsia (PE), a condition characterized by elevated blood pressure and the presence of protein in the urine occurring beyond the 20th week of pregnancy. METHODOLOGY: The case-control investigation spanned 10 months, following the acquisition of informed consent and the receipt of ethical clearance. The study sample comprised a total of 70 pregnant women, evenly divided into two groups: 35 cases of PE and 35 normotensive pregnant controls. Both the cases and controls provided 3 ml venous blood samples. The study employed a semi-automated three-part hematological analyzer to establish the baseline RDW for all individuals. RESULTS: This study showed that the individuals with pre-eclampsia had a greater RDW compared to the healthy pregnant women. The observed difference was found to be statistically significant, with a p-value of 0.004. The receiver operating curve (ROC) analysis showed that RDW exhibited significant diagnostic accuracy in differentiating between cases and controls (area under the curve [AUC] = 0.71, P = 0.004) when employing a cut-off value of >= 18.25. The sensitivity was 80% and the specificity was 71.4%. CONCLUSION: In contrast to other indicators of inflammation, RDW is a cost-effective and easily accessible biomarker that can be acquired from routine complete blood counts. It has the potential to be valuable in predicting and diagnosing pre-eclampsia.

Assessment of Malondialdehyde and Organochlorine Pesticides in Aplastic Anemia Severity Groups: Insights Into Oxidative Stress and Exposure.

Background There is little evidence that pesticide exposure is the primary cause of acquired aplastic anemia (AAA), even though the prevalence of aplastic anemia (AA) is substantially higher in underdeveloped countries than in affluent countries. AA caused by pesticides has not yet been fully understood. This study aimed to examine the potential link between plasma levels of malondialdehyde (MDA) and organochlorine pesticides (OCPs) as risk factors for developing AAA in the North Indian population. Methods This case-control study was conducted at a tertiary care hospital in North India. A total of 99 participants were chosen for the study, of whom 45 were cases of AA. These cases attended the Clinical Hematology department over a period of 1.5 years (May 2018 to November 2019). Forty-five controls were age and sex-matched, apparently healthy subjects. Written informed consent was obtained from each subject before performing the study. Exclusion criteria included patients unwilling to give consent, those using medication to treat AA, those genetically predisposed to AA, those with characteristics including granuloma and dysplasia of bone marrow, any other systemic illness, and subjects with a history of smoking, drinking, or using tobacco in any form. Gas chromatography-tandem mass spectrometry (GC-MS/MS) was used to evaluate the plasma levels of organochlorines. The estimation of plasma MDA, i.e., the lipid peroxide content, was measured. Results The severity of AA is significantly associated with plasma levels of α-Hexachlorocyclohexane (p = 0.040), Heptachlor (p = 0.006), Aldrin (p < 0.001), p,p'-Dichlorodiphenyldichloroethane (p = 0.004), Endosulfan sulfate (p = 0.010), and Methoxychlor (p = 0.001). There was a statistically non-significant difference in MDA levels between cases and controls (p = 0.145); however, a statistically significant linear increase in MDA levels (p < 0.001) was observed according to the severity of AA. Conclusion Our study suggests that oxidative stress may be linked to the severity of AA. Pesticide exposure (plasma organochlorine levels) could act as a stressor, potentially initiating an alarmin response of oxidative stress in the form of lipid peroxidation (MDA) from damaged tissue, which could then lead to suppression of hematopoiesis and be a possible factor in the development of AA.

Electrical disturbance in heart by smokeless tobacco.

Smokeless tobacco use in the form of chewed tobacco or snuff is common in various parts of the world, including India. It is well known that smokeless tobacco consumption is responsible for cancer but less is known about its role as a risk factor for cardiovascular disease. Nicotine, the main constituent of tobacco smoke is responsible for the elevated risk of the cardiovascular disease and sudden coronary death associated with smoking, presumably by provoking cardiac arrhythmias. This review discusses some of the acute and chronic cardiac effects of smokeless tobacco on cardiovascular disease with special reference to the electrical disturbance as well as comparing nicotine kinetics between smoking and smokeless tobacco. It would further enhance the clamor to urge people to quit all forms of tobacco consumption.

Plasma Levels of Organochlorine Pesticides and Tumor Necrosis Factor-Alpha: A Potential Risk Factor for Developing Acquired Aplastic Anemia in the North Indian Population.

Background Pesticide exposure might have a contributory role in the development of acquired aplastic anemia (AA). However, the precise mechanisms of pesticide-induced AA remain unknown. In this case-control study, we conducted a comparative analysis of plasma levels of organochlorine pesticides (OCP) and tumor necrosis factor-alpha (TNF-alpha) between Indian patients diagnosed with AA and an age- and sex-matched control group. Methods This is an observational case-control study conducted at a tertiary care hospital in North India. In this study, 90 subjects were included, out of which 45 were diagnosed with AA according to the criteria of the International Agranulocytosis and Aplastic Anemia Study. Cases were compared with 45 controls. A trained interviewer gave all study subjects a questionnaire to collect data regarding demographic details, exposure to pesticides, and clinical history. Physical examination and routine laboratory investigations of each subject were performed. Both cases and controls were tested for their plasma levels of organochlorines as per established protocol by gas chromatography-mass spectrometry. TNF-alpha level was measured by enzyme-linked immunosorbent assay in each subject. Results There was a significant increase in plasma levels of delta hexachlorocyclohexane (delta HCH) (p = 0.02) and heptachlor (p = 0.00) in patients with AA as compared to controls. We observed nonsignificant trends towards higher levels of beta HCH (p = 0.643), aldrin (p = 0.399), and p,p'-Dichlorodiphenyltrichloroethane (p,p'-DDT) (p = 0.453) in patients with AA when compared to the controls. There were significantly higher TNF-alpha levels (p = 0.024) in cases as compared to the controls. Conclusion Our study concludes that patients with AA exhibited higher levels of delta-HCH, heptachlor, and TNF-alpha in comparison to the control group. There is a significant positive correlation of TNF alpha with OCPs (alpha HCH, lindane, delta HCH, heptachlor, aldrin, p,p'- DDD, and methoxychlor pesticides). These organochlorines may have accumulated in the fatty tissue of bone marrow because of their lipophilic nature. This suggests that they might have served as a neoantigen to trigger an increase in TNF-alpha production, which may have led to disrupted bone marrow function through cell-mediated immunity, leading to AA.

Impedance cardiography for monitoring changes in cardiac output.

Impedance Cardiography (ICG) is a non invasive method useful for continuous monitoring of cardiac output but, it still has not found wide usage for measuring cardiac output in clinics and research. Most studies focused on comparing the cardiac output measured at rest with reference methods. In the present study we evaluated the validity of ICG against Doppler Echocardiography (DE) in measuring cardiac output changes that occur during static exercise. Cardiac output of 30 healthy males between 18-26 yrs of age was measured during supine rest, during and 5 min after completion of 3 minute static exercise by ICG and DE. The increase in cardiac output during exercise measured with ICG and DE does not differ significantly (1.04 +/- 0.72 L/min and 1.05 +/- 1.24 L/min respectively) and has significantly high correlation (r = 0.76, P < 0.001). The bias and limits of agreement are (-0.01 +/- 0.83) in acceptable limits. The pooled means of cardiac output measured by ICG and DE do not differ significantly and bears a significant correlation (r = 0.812, P < 0.001). The bias (d +/- s) calculated is 0.15 +/- 0.64 L/min. ICG could provide valid information regarding the relative changes in cardiac output.

Effect of examination stress on mood, performance and cortisol levels in medical students.

Stress produces definable mental and physiological reactions in the body. Mild stress is beneficial in cognitive tasks and performance but persistently high stress may lead to neuropsychiatric illnesses like anxiety and depression. Examinations act as stressor and activate hypothalamic-pituitary adrenal axis causing an increase in cortisol level, which is reflected in saliva. Present study was done on 35 medical students. Their mood parameters were assessed, using Depression Anxiety Stress Scale (DASS) scoring, and salivary cortisol levels using quantitative ELISA. Subjects were evaluated for mood parameters two times, one during relaxed state (with no examinations in preceding 2 weeks and in coming 2 weeks) and another during stressed state (on the day of viva voce examination). The levels of mood parameters and salivary cortisol were significantly raised during examination stress. The changes in stress level significantly correlated with change in levels of anxiety and salivary cortisol though there was no significant effect on the performance. Males and females showed similar changes in mood parameters. This study suggests that as examinations act as unavoidable stressors, the medical educators as well as students should be made aware of the negative consequences of stress faced during medical training. Efficient relaxation program as well as counseling services should be provided to stressed students so that they are able to cope better with examination stress.

Comparison of frequency domain parameters of heart rate variability between women with polycystic ovarian disease and apparently healthy women.

Background: Polycystic ovary syndrome (PCOS) patients shows common features like increased insulin resistance and adiposity, which have been known to correlate with sympathetic hyperactivity. Objective: The aim of this study is to analyze the characteristics of heart rate variability in women with PCOS. To compare frequency domain parameters of heart rate variability (HRV) between women with PCOS and apparently healthy women. To study the impact of cardiometabolic parameters such as BMI and blood pressure on frequency-domain HRV parameters. Methods: A total of 30 women with PCOS aged 20 to 40 years (as per Rotterdam criteria) were enrolled as cases and 30 age-matched women having normal ovulatory cycles were enrolled as controls. HRV was recorded using an electrocardiography machine (ECG) machine. The following frequency-domain parameters were assessed: Total power, Very low frequency (VLF), VLF%, Low Frequency (LF), LF%, LF nu, High frequency (HF), HF%, HF nu, LF/HF ratio, short-term variability (SD1), and long-term variability (SD2), respectively. Results: Mean age of cases was 28.03 ± 5.33 years. Mean BMI of PCOS women was 25.39 ± 2.69 kg/m2. A total of 18 (60%) had BMI >25 kg/m2. Cases had significantly higher BMI, waist hip ratio, and blood pressure as compared with controls. None of the controls had BMI >25 kg/m2. Majority of cases (66.7%) had systolic blood pressure/diastolic blood pressure (SBP/DBP) >130/85 mmHg as compared with only 6 (20%) of controls (P < 0.001). For different frequency domain parameters, no statistically significant difference between two groups was observed for VLF and LF. Mean VLF%, LF%, LF (nu), and LF/HF were significantly higher in cases as compared with controls. For all, the other mean value was significantly lower in cases as compared with that of controls (P < 0.05). Conclusions: Autonomic nervous system is affected by PCOS status of women, and sympathetic hyperactivity is seen.

Sampling rate influences measures of blood pressure variability in ambulatory blood pressure monitoring.

BACKGROUND: Ambulatory blood pressure monitoring (ABPM) is a valuable tool in the diagnosis and management of hypertension and it is a good predictor of future cardiovascular events. Lack of normal threshold values of ABPM parameters and inconsistency in the sampling rate of recording are hurdles in its wider usage. The aim of the present investigation was to study the influence of sampling rate on ABPM. METHODS: ABPM was performed in 47 healthy subjects and the effect of different sampling rates was studied on ABPM parameters. RESULTS: When data were down-sampled, there was a trend towards decreased concordance and increased dispersion with less frequent recordings. Percent dispersion of MESOR, 24-h average, 24 h standard deviation (SD), awake hours average and sleep hours average of systolic BP (SBP) were around 10% for a sampling interval of 1 h. While average real variability (ARV), morning surge and percent dip in SBP exhibited more than 30% dispersion at a sampling interval of 30 min. CONCLUSION: 24-h average blood pressure (BP) is less sensitive to sampling rate whereas BP variability parameters such as ARV, morning surge and percent dip in SBP are highly sensitive. We suggest that for improving the accuracy of BP variability parameters, a higher sampling rate is desirable around the time of awakening (~2 h before and after the expected time of awakening). At other times, a lower sampling rate may be used for maximizing patient comfort without compromising measurement accuracy.

Association of sleep duration and sleep quality with body mass index among young adults.

Background: It is evident from the research in recent years that short sleep has been found as a risk factor for obesity. However, we still need enough evidence in this field. Therefore, we explored the directionality of the association between sleep duration and sleep quality with body mass index (BMI). Aims: The aim of this study is to evaluate the association of sleep duration and sleep quality with BMI among young adults. Objectives: (a) To assess the association of sleep duration with BMI. (b) To assess the quality of sleep with BMI. Methods: In this cross-sectional study, 88 individuals selected from King George's Medical University were taken as participants. Majority of patients were males (67%). There were 29 (33.0%) females. Sex ratio of study was 2.03, and we used Pittsburgh sleep quality index (PSQI) questionnaire to assess time spent in bed and sleep quality. BMI was divided into 3 categories. Underweight (BMI <18.5 kg/m2), normal weight (18.5-22.9 kg/m2), overweight (23-24.9 kg/m2), obese grade I (25-34.9 kg/m2), obese grade II (35.0 kg/m2), and above. Results: We observed that short sleep duration ± SD (h) <6 h/day f = 9.04; P < 0.001 is associated with greater chances of being overweight and obese and mean sleep quality (mean PSQI ± SD) f = 12.24; P < 0.001 was poor in obese grade I and II. Mean neck and waist circumference also showed a significant increasing trend with increasing BMI category (P < 0.001). Conclusion: This study concludes that short sleep duration and poor sleep quality were associated with overweight obesity among young adults.

Leptin DNA Methylation and Its Association with Metabolic Risk Factors in a Northwest Indian Obese Population.

BACKGROUND: It is well established that obesity is a major health risk in diabetes and associated diseases. Epigenetic changes, specially DNA methylation, play an important role in regulation of adipokines. The objective of the present study was to evaluate the DNA methylation status at the promoter region of the leptin gene in obese individuals and its association with metabolic risk factors. METHODS: The study included obese (n=100) and non-obese (n=75) individuals aged 25-45 years, and measured their physical, biochemical parameters (glucose, insulin, and lipid profiles) and leptin, DNA methyltransferase 1 (DNMT1), and DNA methyltransferase 3 beta (DNMT3b) mRNA expressions with real-time reverse transcription-polymerase chain reaction (qRT-PCR). DNA methylation of the leptin gene at the promoter region was analyzed by methyl-specific qPCR . RESULTS: The study found that the DNA methylation level at the promoter area of the leptin gene was negatively associated with weight in obese subjects. Furthermore, study findings showed that the DNA methylation level was negatively associated with fasting insulin, glucose, homeostatic model assessment for insulin resistance, and total cholesterol. There was also a higher expression of DNMT1 and DNMT-3b in obese subjects as compared with non-obese subjects. CONCLUSION: The leptin epigenetic profile may be associated with obesity and its associated metabolic risk factors.

Correlation of obesity indices with heart rate recovery as a marker of autonomic function in healthy young adults.

INTRODUCTION: Obesity has become a challenge for global public health. The global prevalence of obesity has nearly doubled in the past decades (World Health Organization). Obesity may lead to changes in the sympathetic regulation of cardiovascular function, thus favoring the development of cardiovascular complications. AIM: To find a correlation between various obesity indices (body mass index, waist-height ratio, waist circumference and waist-hip ratio) and heart rate recovery in healthy subjects. MATERIALS AND METHODS: A total of 100 apparently healthy subjects aged 18-30 years were enrolled and were divided into two groups on the absence and presence of a family history of cardiovascular disease. The treadmill testing was done in the exercise lab of the physiology department of the medical institute. Exercise testing of the subjects was conducted according to the standard Bruce protocols. RESULTS: There was a negative correlation between various obesity indices and heart rate recovery but we did not get a statistically signification association between them. CONCLUSION: In our study, we have found no statistically significant association between various obesity indices and heart rate recovery. Thus measuring obesity indices in the younger age group will not lead to much significance in terms of heart rate recovery and may be avoided.

Outbreak Trends of Coronavirus Disease-2019 in India: A Prediction.

OBJECTIVE: The objective of this paper is to prepare the government and citizens of India to take or implement the control measures proactively to reduce the impact of coronavirus disease 2019 (COVID-19). METHOD: In this work, the COVID-19 outbreak in India has been predicted based on the pattern of China using a machine learning approach. The model is built to predict the number of confirmed cases, recovered cases, and death cases based on the data available between January 22, 2020, and April 3, 2020. The time series forecasting method is used for prediction models. RESULTS: The COVID-19 effects are predicted to be at peak between the third and fourth weeks of April 2020 in India. This outbreak is predicted to be controlled around the end of May 2020. The total number of predicted confirmed cases of COVID-19 might reach around 68 978, and the number of deaths due to COVID-19 are predicted to be 1557 around April 25, 2020, in India. If this outbreak is not controlled by the end of May 2020, then India will face a severe shortage of hospitals, and it will make this outbreak even worse. CONCLUSION: The COVID-19 pandemic may be controlled if the Government of India takes proactive steps to aggressively implement a lockdown in the country and extend it further. This presented epidemiological model is an effort to predict the future forecast of COVID-19 spread, based on the present scenario, so that the government can frame policy decisions, and necessary actions can be initiated.

Circadian rhythm of airways caliber and its autonomic modulation.

The autonomic nervous system (ANS) is one of the effector pathways for circadian variation of many physiological parameters. Autonomic tone and airways caliber have been reported to exhibit circadian variation in separate studies. A simultaneous investigation of heart rate variability (HRV) and airway caliber might ascertain how airway caliber is modulated by autonomic tone. This study was planned to identify the variations in airway caliber and autonomic function tone during a 24-hour span. A total of 56 healthy male subjects with almost similar daily routines were studied. Time domain, frequency domain and nonlinear analysis of R-R interval from 5 min electrocardiogram (ECG) was done seven times during the daytime wake span at 3-hour intervals starting at 05:00 h in the morning until 23:00 h in the night. Simultaneously peak expiratory flow rate (PEFR) was determined using a mini Wright's peak flow meter. Rhythmometric analysis was done for PEFR and HRV parameters. Significant circadian variation in low frequency (LF) and high frequency (HF) variance was identified in this group of healthy subjects. The circadian rhythm of LF variance was characterized by a gradual increase and corresponding reciprocal change in HF variance from morning until night. The LF/HF ratio and SD2/SD1 ratio reflecting sympatho-vagal balance showed low to high values from morning to evening. The acrophase of the PEFR temporal pattern is similar to that of LF power and almost opposite in phase to that of HF power. PEFR is positively correlated with LF power. The circadian rhythm of airway caliber co-varies with cardiac autonomic tone. It appears that the temporal pattern of cardiac autonomic tone precedes in time that of airways caliber, thereby suggesting the latter operates under the modulatory effect of the 24-hour pattern in sympatho-vagal balance.