Impairment of the baroreflex control of human respiratory resistance with age

Tafil-Klawe M, Klawe Jj, Zalewski P, Lewandowski, Lewandowski A

Description

The mechanism responsible for the central baroreflex resetting with age are an area of limited knowledge. We previously demonstrated that in subjects aged above 50 the airway resistance did not change in response to baroreceptor activation, whereas in younger volunteers the airway resistance significantly decreased. Objective The aim of the present study was to evaluate the effect of carotid baroreceptor inactivation on the reflex change of respiratory resistance, in the course of aging. Materials and methods 80 healthy men, divided in four groups: aged 20-30 (Group I), 31-40 (Group II), 41-50 (Group III), and 51-60 (Group IV) were included in the study. The selective inactivation of carotid baroreceptors was induced by generating a positive pressure of 40 mmHg for 5 s in two capsules placed bilaterally on the neck over the bifurcation of the carotid arteries. The oscillatory method (Siregnost FD5, Siemens) was used to measure continuously respiratory resistance. Results Inactivation of carotid baroreceptors produced a short increase in respiratory resistance by 0.38 ± 0.01SE mbar/l/s, i.e., 21.7% above the resting level in Group I and by 0.25 ± 0.01 mbar/l/s in Group II. In the two older groups (III and IV) respiratory resistance did not change in response to baroreceptors inactivation. Conclusions In humans aged above 40, carotid baroreceptors do not contribute to bronchodilator tone, which causes imbalance between the activities of upper airway and chest wall inspiratory muscles leading to a collapsing effect on the upper airway.

Sujets

• Ageing
• Airway resistance
• Baroreflex

Informations

• Publié par: biomed
• Publié le: 01 janvier 2009
• Nombre de lectures: 6
• Langue: English

Extrait

1 2 Department ofHuman Physiology, Medical Faculty andDepartment ofHygiene and Epidemiology, Faculty ofHealth Sciences and 3 Department ofBasis ofPhysical Education, Faculty ofHealth Sciences, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Torun, Poland

© I. Holzapfel Publishers 2009

241

M ATERIAL AND M ETHODS

cates a central defect, demonstrated in animal studies free ofatherosclerosis and hypertension [4, 5, 6]. The mechanisms responsible for central baroreflex reset- ting with age probably involve enhanced interaction between the hypothalamic centers and the solitary tract nucleus, and an exaggerated central adaptation to baroreflex input [7, 8]. Our previous study showed that selective carotid baroreceptors activation decreas- es airway resistance in humans 20-40 years old, where- as this response did not occur in older subjects [9, 10]. The aim ofthe present study was to evaluate the ef- fect ofcarotid baroreceptor inactivation on the reflex change ofrespiratory resistance in the course ofag- ing.

In order to inactivate carotid baroreceptors a two- neck-chamber method was applied. Selective inactiva- tion ofcarotid baroreceptors was induced by generat- ing a positive pressure of40 mmHg for 5 s in two capsules placed bilaterally on the neck over the bifur- cation ofthe carotid arteries. The stimuli were applied 250 ms after the R-wave during the expiratory phase of breathing.The maximal rate ofair pressure in- crease was 300 mmHg per second. The following vari- ables were recorded continuously: • R-Rintervals, measured from ECG; • Respiratoryphase and the rate ofbreathing by means ofa termistor placed at the nose orifice; • Airpressure in the neck chambers.

Abstract Backgr ound:The mechanism responsible for the cen- tral baroreflex resetting with age are an area oflimited knowledge. We previously demonstrated that in sub- jects aged above 50 the airway resistance did not change in response to baroreceptor activation, where- as in younger volunteers the airway resistance signifi- cantly decreased. Objective:the present study was to evalu-The aim of ate the effect ofcarotid baroreceptor inactivation on the reflex change ofrespiratory resistance, in the course ofaging. Material and methods:80 healthy men, divided in four groups: aged 20-30 (Group I), 31-40 (Group II), 41-50 (Group III), and 51-60 (Group IV) were included in the study. The selective inactivation ofcarotid barore- ceptors was induced by generating a positive pressure of 40mmHg for 5 s in two capsules placed bilaterally on the neck over the bifurcation ofthe carotid arter- ies. The oscillatory method (Siregnost FD5, Siemens) was used to measure continuously respiratory resist- ance. Results:Inactivation ofcarotid baroreceptors pro- duced a short increase in respiratory resistance by 0.38 ± 0.01SE mbar/l/s, i.e., 21.7% above the resting level in Group I and by 0.25 ± 0.01 mbar/l/s in Group II. In the two older groups (III and IV) respiratory resist- ance did not change in response to baroreceptors inac- tivation. Conclusions:In humans aged above 40, carotid barore- ceptors do not contribute to bronchodilator tone, which causes imbalance between the activities ofup- per airway and chest wall inspiratory muscles leading to a collapsing effect on the upper airway. Key words:aging, airway resistance, baroreflex, upper airway I NTRODUCTION Numerous studies in humans have demonstrated im- pairment ofbaroreflex control ofheart rate with ad- vancing age [1, 2, 3]. Studies in animal models showed decreased baroreceptor sensitivity by direct electro- physiological recordings ofbaroreceptor discharges [4]. Reduced reflex response during equivalent levels of baroreceptorinput, showed in other studies, indi-

EUROPEAN JOURNAL OF MEDICAL RESEARCH

Eur J Med Res (2009) 14(Suppl. IV): 241-243

December 7, 2009

I NACTIVATION OF C AROTID B ARORECEPTORS

The study was approved by a local Ethics Committee and was performed in accordance with the Helsinki Declaration for Human Research. Eighty male sub- jects were enrolled into the study. Table 1 demon- strates four age-differentiated groups ofsubjects. All subjects were healthy, normotensive, and non-smok- ers. Subjects with a history ofsnoring or exceeding 150% ofideal body weight were excluded from the study in order to avoid the effects ofsnoring or obe- sity on the cardiovascular system. All experiments were performed at rest in the seated recumbent posi- tion.

I MPAIRMENT OF T HE B AROREFLEX C ONTROL OF H UMAN R ESPIRATORY R ESISTANCE WITH A GE

1 22 3 M. Tafil-Klawe , J. J. Klawe , P. Zalewski , A. Lewandowski