The Effects Of Bronchodilator Therapy On Respiratory And Autonomic Function In Patients With Familial Dysautonomia

Overview

Evaluate the effects of bronchodilator therapy on respiratory function. Our overall goal is to determine whether, in patients with familial dysautonomia (FD), there is a component of airway obstruction that is reversible. To this end, we will evaluate airway resistance before and after receiving the anti-cholinergic ipratropium (Atrovent ®) and the beta-2-agonist albuterol (ProVentil®/Ventolin®). We predict that the response to either drug will depend on the underlying level of sympathetic and parasympathetic activity and airway tone. We will then determine the cardiovascular effects of inhaled ipratropium and albuterol in patients with FD. Because patients with FD have fewer sympathetic neurons and denervation supersenstivity, we predict that following albuterol inhalation, there will be non-selective activation of alpha-1-adrenergic receptors. Furthermore, because of a congenital defect in the afferent baroreceptor neurons that sense blood pressure, we suspect that the resulting vasoconstriction will be unopposed leading to a pressor effect. We hypothesize that inhalation of the anti-cholinergic ipratopium will produce little rise in heart rate, due to the extent of parasympathetic denervation to the heart.

Familial dysautonomia (FD) is a rare fatal autosomal recessive disease caused by a deficiency of the protein IKAP.1 This results in a selective developmental defect that affects mostly afferent (sensory) neurons including those in the dorsal root ganglia and cranial nerves.2, 3 We have shown recently that the protein deficiency impairs the development of afferent baroreceptor pathways, leaving the sympathetic efferent neurons reduced in number but functionally active. This results in the complete failure to detect and buffer fluctuations in blood pressure leading to volatile hypertension. In addition to the afferent baroreflex pathways, the deficiency of IKAP during embroyogenesis also affects the function of the chemoreflex pathways. As a result, patients fail to increase ventilation adequately in response to hypoxia and hypercapnia.4 As well as the impairment of the neurological mechanisms that regulate breathing, patients with FD also have a combination of obstructive, restrictive and probably also neuromuscular lung disease. Failure to coordinate swallowing results in recurrent bouts of aspiration pneumonia occurring from birth.5, 6 Imaging studies show that almost all patients with FD have bronchial wall thickening, atelectasis and almost 30% have bronchiectasis7. Pulmonary function tests show air flow limitation and associated lung restriction with reduction in diffusion capacity12. Sudden attacks of asthma like wheezing are common 8 and frequently associated with emotional upset,5 a time when sympathetic outflow to the vasculature is increased heightened.3 There is also a component of restrictive lung disease, with a very high incidence of scoliosis, which frequently begins at an early age. Complicating matters further, many patients opt to undergo spine fusion surgery, 9 which could potentially worsen further chest wall compliance.10 Patients with FD also lack muscle spindles, 2 making it likely that they have neuromuscular abnormalities arising from the absence of proprioceptive feedback from the respiratory muscles involved in the coordination of breathing. Severe respiratory disease is a leading cause of death in patients with FD and many are treated empirically with inhaled bronchodilators. It is not known, however, whether these drugs are effective at reversing increased airway resistance. Hence, there is an urgent need to understand if the short acting beta-2-adrenergic agonist albuterol and the anticholinergic ipratropium, are effective bronchodilators. Furthermore, because treatment with these agents has potential cardiovascular side effects, we will also analyze their effects on blood pressure, heart rate and cardiac output.