Ashok Kumar Jaryal

Assessment of heart rate variability derived from finger-tip photoplethysmography as compared to electrocardiography

Heart rate variability (HRV) is traditionally derived from RR interval time series of electrocardiography (ECG). Photoplethysmography (PPG) also reflects the cardiac rhythm since the mechanical activity of the heart is coupled to its electrical activity. Thus, theoretically, PPG can be used for determining the interval between successive heartbeats and heart rate variability. However, the PPG wave lags behind the ECG signal by the time required for transmission of pulse wave. In this study, finger-tip PPG and standard lead II ECG were recorded for five minutes from 10 healthy subjects at rest. The results showed a high correlation (median = 0.97) between the ECG-derived RR intervals and PPG-derived peak-to-peak (PP) intervals. PP variability was accurate (0.1 ms) as compared to RR variability. The time domain, frequency domain and Poincaré plot HRV parameters computed using RR interval method and PP interval method showed no significant differences (p < 0.05). The error analysis also showed insignificant differences between the HRV indices obtained by the two methods. Bland-Altman analysis showed high degree of agreement between the two methods for all the parameters of HRV. Thus, HRV can also be reliably estimated from the PPG based PP interval method.

Heart rate variability and autonomic function tests in HIV positive individuals in India.

Supine heart rate variability (HRV) and autonomic tests were carried to determine whether autonomic activity was affected in HIV positive patients. The pressor response following handgrip and cold pressor test was blunted in HIV+ patients, and the degree of dysfunction correlated with CD4 cell counts. The extent of autonomic impairment was mild and subclinical.

Renal transplantation normalizes baroreflex sensitivity through improvement in central arterial stiffness

BACKGROUND In end-stage renal disease (ESRD) patients, the most common cause of mortality and morbidity are cardiovascular events. This could be attributed to the impaired baroreflex function observed in this group of patients. The effect of renal transplantation (RT) on the baroreflex sensitivity (BRS) in ESRD patients has been inadequately addressed. Therefore, we investigated baroreflex function and its relation to arterial stiffness indices and cardiovascular variability parameters (heart rate and blood pressure variability--HRV and BPV) in ESRD patients before and after transplantation to decipher the underlying mechanism of attenuated BRS in ESRD patients. METHODS We studied 23 ESRD patients (mean age; 36 years) prospectively before and at 3 and 6 months after RT. Baroreflex function was determined by spontaneous method (sequence and spectral indices). Short-term HRV and BPV were assessed using power spectrum analysis of RR intervals and systolic blood pressure by frequency domain analysis. Arterial stiffness indices were assessed by carotid-femoral pulse-wave velocity (PWV), augmentation index (AI) and central pulse pressure using Sphygmocor Vx device (AtCor Medical, Australia). RESULTS RT was associated with the normalization of BRS by 6 months. Arterial stiffness indices, such as AI and central pulse pressure, showed a significant reduction as early as 3 months after RT. PWV and frequency domain measures of HRV after RT did not show statistically significant changes except the LF/HF ratio which had a significant increase at 6 months when compared with baseline. Systolic BPV total power showed a significant reduction by 3 months after RT. CONCLUSIONS Our data suggest that RT normalizes BRS in ESRD patients by 6 months which follows the improvement in the AI and central pulse pressure.

Decreased autonomic modulation of heart rate and altered cardiac sympathovagal balance in patients with Cushing's syndrome: role of endogenous hypercortisolism.

Background/Aims: Endogenous Cushings syndrome is associated with a higher risk of cardiovascular morbidity and mortality. Previous literature suggested multiple possible links by which hypercortisolism may alter the autonomic control of cardiovascular functions. We investigated the impact of chronic endogenous hypercortisolism on the autonomic regulation of cardiac functions by short-term heart rate variability analysis. Methods: Eighteen patients with endogenous Cushings syndrome and 20 age-, gender- and BMI-matched controls participated in the study. ECG signal was acquired in lead II configuration for 5 min and heart rate variability assessment was made in both time and frequency domain using the extracted RR interval data. Results: All time and frequency domain measures of heart rate variability were significantly (p < 0.05) lower in the patient group compared to the control group. The patient group had an altered sympathovagal balance with low frequency/high frequency band ratio significantly higher than the control group [1.857 (0.6747-2.610) vs. 0.8581 (0.4779-1.352); p = 0.0253]. A significant negative correlation was obtained between normalized high frequency power of heart rate variability and basal cortisol levels (r = -0.6594; p = 0.0029). Multiple linear regression analysis identified age, disease duration (in months), basal cortisol levels and systolic blood pressure as independent predictors of normalized high frequency power. Conclusion: Findings of the study clearly portrayed the diminished autonomic modulation of heart rate in endogenous Cushings syndrome and its possible relationship with hypercortisolism as the main causative factor. Diminished heart rate variability may be an indicator of the increased risk of cardiac mortality in these patients.

Baroreflex dysfunction in chronic kidney disease.

Chronic kidney disease (CKD) patients have high cardiovascular mortality and morbidity. The presence of traditional and CKD related risk factors results in exaggerated vascular calcification in these patients. Vascular calcification is associated with reduced large arterial compliance and thus impaired baroreflex sensitivity (BRS) resulting in augmented blood pressure (BP) variability and hampered BP regulation. Baroreflex plays a vital role in short term regulation of BP. This review discusses the normal baroreflex physiology, methods to assess baroreflex function, its determinants along with the prognostic significance of assessing BRS in CKD patients, available literature on BRS in CKD patients and the probable patho-physiology of baroreflex dysfunction in CKD.

Correction for Blood Pressure Improves Correlation between Cerebrovascular Reactivity Assessed by Breath Holding and 6% CO2 Breathing

BACKGROUND Changes in cerebral blood flow velocity to hypercapnia are associated with changes in systemic blood pressure (BP). These confounding BP-dependent changes in cerebral blood flow velocity cause misinterpretation of cerebrovascular reactivity (CVR) results. The objective of the study was to determine the relationship between CVR assessed by breath holding and 6% CO2 breathing after correcting for BP-dependent changes in cerebral blood flow velocity. METHODS In 33 patients of uncomplicated type 2 diabetes mellitus, CVR was assessed as percentage changes in cerebral blood flow velocity and cerebrovascular conductance index. RESULTS Percentage change in cerebral blood flow velocity during breath holding was positively correlated with that of during 6% CO2 breathing (r = .35; P = .0448). CVR during breath holding and 6% CO2 breathing were better correlated when expressed as percentage changes in cerebrovascular conductance index (r = .49; P = .0040). Similarly, breath-holding test results expressed as percentage changes in cerebral blood flow velocity correctly identified only 37.5% of the poor reactors to 6% CO2 breathing. However, when the breath-holding test results were expressed as percentage changes in cerebrovascular conductance index, 62.5% of the poor reactors to 6% CO2 breathing were correctly identified indicating a better agreement between the test results obtained by the 2 methods. CONCLUSION Cerebrovascular response to breath holding is better correlated with that of 6% CO2 breathing when changes in cerebral blood flow velocity were corrected for associated changes in BP.

Influence of respiratory rate on the variability of blood volume pulse characteristics

Photoplethysmogram (PPG) measures have been proven useful for the quantification of sympathetic reactivity and continuous monitoring of vascular reactivity. This study was designed to delineate the influence of respiratory rate on the variability of various PPG characteristics in time and frequency domains. PPG, electrocardiogram (ECG) and respiration were simultaneously recorded for 2 min from eight healthy volunteers during paced respiration of 6, 12 and 18 cycles min−1. The PPG characteristics such as peak-to-peak interval (PPI), systolic peak amplitude, slope, Tcrest, Tdecay and pulse transit time (PTT) were computed for every pulse. In time domain, the mean of amplitude, slope and Tcrest were not significantly different amongst three different respiratory rates. However, the mean of Tdecay, PPI and PTT were significantly increased (p < 0.05, p < 0.05 and p < 0.01, respectively) during respiration of 6 cycles min−1 compared to 12 cycles min−1. The maximal spectral powers of the variability of all PPG measures were centred on the respiratory frequency in frequency domain. In conclusion, the results that the amplitude and slope in time domain are not altered by the respiratory frequency suggest their application in faithful assessment of cardiovascular reactivity. As the variability of PPI, Tdecay and PTT are altered by the slow respiration, the influence of respiration on these time derivatives should not be ignored during interpretation of vascular reactivity.

Idiopathic Harlequin Syndrome A Pediatric Case

Harlequin syndrome, Harlequin sign, Holmes-Adie syndrome, and Ross syndrome lie on a spectrum of partial dysautonomias affecting facial sudomotor, vasomotor, and pupillary responses. These syndromes have imprecise clinical boundaries and overlap syndromes are known. We report a 9-year-old girl who presented with anhidrosis over the right half of her face and the left side of her body, with compensatory hyperhidrosis on the contralateral side. She was noted to have bilateral tonic pupils and normal muscle stretch reflexes with other features suggestive of autonomic dysfunction. Investigations to rule out secondary causes were noncontributory. Her clinical presentation can be categorized as partial overlap between Harlequin syndrome and Holmes-Adie syndrome.

Monitoring of Cardiovascular Reactivity During Cold Pressor Test Using Photoplethysmography

Cold pressor test (CPT) is a standard autonomic function test to assess the sympathetic activity. The rise in diastolic blood pressure, secondary to the vasoconstriction in the peripheral vessels has been traditionally used to quantify the sympathetic reactivity to cold stimulus. In the present study, the ongoing short-term changes in vascular condition during CPT have been directly studied using waveform analysis of infrared finger-tip photoplethysmogram (PPG). Electrocardiogram (ECG) and PPG were simultaneously recorded from 11 healthy volunteers in resting condition (1 min), during (1 min) and after (5 min) the test. The PPG characteristics such as peak-to-peak interval (PPI), peak amplitude, slope, crest time and decay time were computed for every PPG pulse. In addition, the beat-to-beat changes of pulse wave transit time (PTT) representing the vascular compliance were also computed. The results depicted that the mean PPI, decay time and PTT were significantly different (respectively p≪0.01, p≪0.05 and p≪0.01) during CPT compared to rest. A sharp significant change was noticed in the amplitude (3.77±1.50 to 0.90±0.41 V) and slope (48.39±23.86 to 12.33±6.05 V/s) in response to the cold stimulus followed by a slow recovery phase. These results suggest that PPG based objectively derived parameters can be used for quantification of sympathetic reactivity and for continuous monitoring of vascular reactivity.

Comparison of heart rate variability among children with well controlled versus refractory epilepsy: A cross-sectional study

PURPOSE Autonomic symptoms frequently occur during seizures. There are reports that the adult group of intractable epilepsy patients have different autonomic profile than the well controlled epilepsy, but there is no clear evidence in the children epilepsy group, therefore, we planned to study the autonomic profile in well controlled and refractory epilepsy children by recording the short-term heart rate variability (HRV). METHODS This cross sectional study was conducted in a tertiary care hospital between July 2008 and June 2009. Children with mean age of 9.1±3.3 years were enrolled. Three groups of children, 40 in each group namely, refractory epilepsy, well controlled epilepsy and normal control children were included. Children who had chronic systemic diseases and were on drugs that cause autonomic dysfunction were excluded. All children underwent short term heart rate variability testing. Data was analyzed in time domain and frequency domain. RESULTS pNN50 was significantly lower in children with refractory epilepsy than the well control as well as healthy controls. Rest of the parameters of time domain and frequency domain were comparable between the groups. CONCLUSIONS Our study showed that parasympathetic activity is lower in refractory epilepsy children. However, autonomic tone is comparable in well control versus healthy controls.