DISCUSSION The present study was conducted to assess the sympathetic reactivity by blood pressure response to static exercise among the medical students with parental history of hypertension. Audiovisual reaction time & anxiety levels were also studied in these children. In the present study it was observed that 81.67% students had a history of hypertension in either parent, out of whom 58.4% students had a history of hypertension in father & 23.3% students had a history of hypertension in mother & 18.33% students had history of hypertension in both the parents. The strength of hereditary risk in causation of diseases doubles with single first degree hypertensive relative & quadruples with two such relatives.
73Some studies in the past have reported the probability of developing hypertension in the offspring’s of hypertensive parents in future to be 25%, if the children had history of hypertension in either of the parent ; 50%, if children had history of hypertension in both the parents. 15 This indicates major role of genetics in acquiring the disease even though many confounding factors such as age, gender, lifestyle, stress ; environmental factors also play an important role in causation of disease. 74 Johns Hopkins Precursors Study also reported a strong incidence of acquiring hypertension in adult life with history of hypertension in both parents. 75 In the present study BMI score, resting PR ; BP was slightly higher among children of hypertensive parents. Many studies have found significant rise in BMI ; SBP in the genetically susceptible individuals who inherit these traits as recessive inheritance from either or both parents suffering from hypertension. 14,76 Many other studies observed that the offspring’s of hypertensive parents showed altered lipid profile along with elevated PR, DBP & mean arterial blood pressure (MABP) levels which was found to be more pronounced in consanguineous population. The underlying mechanism was explained on the basis of increased sympathetic activity in these children with high plasma catecholamine levels before exercise.
77, 78, 79 Sympathetic overactivity & high BMI mutually influence the ongoing pathophysiological processes & act as an additional triggering factor to already existing vasoconstriction & retention of sodium due to increased renal sympathetic activity. High level of insulin with increased resistance, raised level of leptin along with free fatty acids & endothelial dysfunction further accelerate the damage associated with sympathetic overactivity. 14, 80 The elevated BP & BMI was also attributed to multiple gene variation & their interactions that regulate BP in response to mental and physical stress. Earlier study reported no change in resting DBP in offspring’s of hypertensive parents in contrast to other study which observed high resting DBP in these children. 81 In the present study there was statistically significant increase in DBP ; SBP during isometric handgrip-test. Rise in systolic ; diastolic blood pressure with hand grip dynamometer is an indicator of increased sympathetic activity. 82 The increased afterload to the heart due to constriction of blood vessels in exercising muscles and increased peripheral vasoconstriction mediated through adrenergic receptors of sympathetic nervous system is responsible for rise in DBP during IHG exercise.
Further the metabolites that accumulate in the exercising muscle like lactic acid and adenosine are sensed by metabosensitive nerve endings in the interstitium of skeletal muscle cause release of afferent discharge of group IV nerves, thus increase the sympathetic reflex activity. Similar observation was reported in few studies earlier, along with high resting PR and BP in children of hypertensive parents. 18, 24 The muscle sympathetic nerve activity, which is under the control of baroreflex shows reduced sensitivity among the children of hypertensive parents. Due to which the sympathetic vasomotor tone is high in them, thus increases the chances of developing hypertension in future. Further explanation for increased peripheral resistance and in turn DBP during IHG exercise is due to sustained muscle contraction that decreases blood flow to the exercising muscle, thus increasing pressure response and perfusion pressure to active muscles. It is also seen that static isometric exercise increases endothelin-1 secretion along with reflex release of nor-epinephrine that is mediated by hypothalamus.
This finding supports the concept of inherited vascular reactivity in the genetically susceptible individuals ; taken as early predictor of development of neurogenic hypertension. 6, 24The high blood pressure reactivity is labeled as biobehavioural risk factor that has harmful effect on cognitive functions like attention, verbal memory ; confrontation naming. 83 Some studies have also reported of high sympathetic activity is associated with reduced cognitive performance. 84 In the present study AVRT was performed to assess cognition ; sensory motor coordination. It was found that students of hypertensive parents showed delayed response to both ART ; VRT of which delayed ART was statistically significant.
Many studies have used audiovisual reaction time as a tool to measure sensory motor intactness, coordination ; information processing speed in middle aged hypertensive cases. The previous study observed longer VRT and impaired cognition in known cases of hypertension. They also found positive correlation between RT ; duration of hypertension, reflecting the harmful effect of elevated BP on nerve conduction velocity in long run. 26 The underlying pathology explained was inflammatory nerve cell injury to basement membrane, axonal degeneration-atrophy ; micro thrombi causing endoneural hypoxia in both slow ; fast conducting fibers.
The peripheral nerves were more vulnerable to early hypertensive changes causing hypertensive neuropathy. The reduced blood supply ; metabolism to the brain tissue was mainly found in the fronto-temporal ; subcortical areas thus affecting cognitive functions in hypertensive patients. The high BP is also damages the blood brain barrier ; hastens the easy accessibility of toxins into the brain tissue. The duration of hypertension is found to be associated with atherosclerotic changes in blood vessels causing hypoxic-ischemia related complications. Many studies on clinical trial have shown improvement in neuropathy ; cognitive functions on proper antihypertensives medication in hypertensive patients. 26 Many studies support the finding of ART to be faster than VRT, as auditory stimuli reaches motor cortex within 8-10 ms ; visual stimuli takes longer time, around 20-40ms for the same. In present study AVRT response was found to be longer for visual red color stimuli ; auditory click stimuli in children of hypertensive.
Many studies on VRT conducted in normotensive individuals in the past have observed contrasting finding for visual red/green color and concluded that reaction time ; chromaticity does not show any correlation. This needs to be further evaluated to study the harmful effect of high blood pressure on chromaticity ; color perception. Though studies on microvascular changes in population aging ; 6years with parental history of hypertension have reported narrowing of retinal arterioles, mainly in female child with associated high prevalence of myopia in them. Though the cause for gender difference is unclear but the vascular changes were attributed to p-selectin mediated activation of C-reactive protein causing platelet adhesion ; endothelial dysfunction. 84, 85, 86 The association between anxiety ; hypertension is investigated in many cross sectional ; prospective studies have given inconsistent results. Some studies reporting anxiety as high risk factor in causation of the disease and some reported even decreased BP in hypertensive patients.
89The present study observed slightly higher levels of anxiety among children of hypertensive parents. To the best of our knowledge/finding/search there is meager literature available that confirms offspring’s of hypertensive parents inherit & exhibit high levels of anxiety. As sympathetic overactivity is associated with high arousal levels, we can say that some amount of anxiety is present in the children of hypertensive parents.
The common emotional relationship & family environment they share also play a role in causation of the disease. Studies in past on assessment of anxiety levels in diagnosed cases of hypertension between 40-60 years age group have found strong association of anxiety and hypertension. Anxiety causes short term increases BP through renin angiotensin system, hypothalamo-pitutary-adernal axis dysfunction with sympathetic over activation causing increased renal water-sodium retention increasing the blood pressure .Also sympathetic overactivity causes abnormal haemodynamic changes and lipid metabolism & endothelial cell damage to increase the blood pressure. 90, 91