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

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.

Inclusion criteria

• 1. Diagnosis of familial dysautonomia (Riley-Day syndrome, hereditary sensory and autonomic neuropathy type III) 2. Ages 12 and older: Bronchodilators are routinely used in young children with FD therefore they should be included in this study. The spirometry maneuver is highly dependent on patient cooperation and effort, and FD patients already have limitations that make the spirometry maneuver more problematic to perform such as difficulty with mouth closure and drooling. Therefore, we believe age 12 is a suitable age for FD patients to be included in this study, though in the general population reliable results can be obtained from the age of 6 and sometimes even younger.

• Patients using Albuterol or Ipratroprium will be included in the study but will be instructed not to take the 24 hours prior to the testing. It is a common practice in clinical medicine to withhold the inhalation drugs prior to performing pulmonary function tests in order to evaluate the response to bronchodilators, an integral part of the test. Patients with an acute respiratory exacerbation will not be enrolled, as withholding bronchodilators would not be advisable.

• Patients who are taking medications that might affect autonomic function such as anti-hypertensives, beta-blockers, midodrine and florinef will be included in the study and we will record current medication regimen and the time the medication was taken.

Exclusion criteria

• 1. Patients who last used inhaled anti-cholinergics or beta-2-agonists within 4-half lives of the drug.

• Patients with an acute respiratory illness 3. Patients who have had lobectomies. 4. Patients using oxygen therapy throughout the day. 5. Patients who are unable to comply with the study requirements.