Ans. a. Cushing's reflex (Ref: Ganong 24/e p607; Schwartz 9/e p1521; Bailey 25/e p483)The triad of hypertension, bradycardia and irregular respiration is seen in Cushing's reflex.'Elevated intracranial pressure, as caused by space occupying lesion like brain tumor or head trauma with associated intracranial bleeding (e.g. epidural /subdural/cerebral- haemorrhage), results in an increased systemic blood pressure (BP) and bradycardiaQ (rather than tachycardia) and irregular breathing. This response is called Cushing's reflex or phenomenon. 'Cushing's TriadIncrease in systolic blood pressureQ (Widening of pulse pressure)Reduction of the heart rateQ (bradycardia)Irregular respirationQ (caused by impaired brainstem function)Cushing ReflexCushing reflex (also referred to as the vasopressor response), is a physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing's triad of increased blood pressure, irregular breathing, and a reduction of the heart rateQ.It is usually seen in the terminal stages of acute head injury and may indicate imminent brain herniationQ.These symptoms can be indicative of insufficient blood flow to the brain (ischemia) as well as compression of arteriolesQ.Etiology:It is a special CNS ischemic response that results from increased intracranial tension (or increased CSF pressure around the brain in cranial vault).Causes of increased ICT may be space occupying lesions such as brain tumorQ, cerebral abscess, head traumaQ with associated intra cranial bleeding (epidural/ subdural/ cerebral-haemorrhage)Pathophysiology:When the ICT or CSF pressure rises to equal the arterial pressure, it compresses the whole brain as well as the arteries in the brain and cuts off the blood supply to the brain, thereby activating the CNS ischemic responseCompromised blood supply, local hypoxia and hypercapnia of RVLM (rostral ventrolateral medulla) neurons or vasomotor area increase their discharge and evoke Cushing's reaction raising systemic arterial pressureQ.Cushing ReflexThe resultant rise in systemic arterial pressure (due to ischemic stimulation of vasomotor regions in medulla) tend to restore the blood flow to medulla, thereby protecting the vital centers of brain from loss of nutrition if ICT rises enough to compress cerebral arteries.The rise in BP is proportional to increase in intracranial tension (over a considerable range) and causes a reflex decrease in heart rate via the arterial baroreceptors. This is why bradycardia rather than tachycardia is characteristically seen in patients with increased intra cranial pressureQ.Bezotd-Jarisch reflex* In experimental animals, injections of serotonin, veratridine, capsaicin, phenyldiguanide. and some other drugs into the coronary arteries supplying the left ventricle cause apnea followed by rapid breathing, hypotension, and bradycardia (the coronary chemoreflex or Bezold-Jarisch reflex).* The receptors are probably C fiber endings, and the afferents are vagal.* The response is not produced by injections into the blood supply of the atria or the right ventricle.Hering-Bruer reflex* The Hering-Breuer inflation reflex is an increase in the duration of expiration produced by steady lung inflation, and the Hering-Breuer deflation reflex is a decrease in the duration of expiration produced by marked deflation of the lung.Bainbridge's reflex* Rapid infusion of blood or saline in anesthetized animals sometimes produces a rise in heart rate if the initial heart rate is low. This effect was described by Bainbridge in 1915, and since then it has been known as the Bainbridge reflex.