Gender Differences in Autonomic Heart Rate Control Mechanisms

Abstract

<p>Cilj ove teze bio je utvrđivanje polnih razlika<br />u mehanizmima vegetativne regulacije srčane<br />frekvencije, kao i utvrđivanje razlika u regulaciji srčane frekvencije kod žena po<br />fazama menstrualnog ciklusa. Kori&scaron;ćeni su<br />parametri varijabilnosti srčanog ritma (heart<br />rate variability) - HRV i oporavka srčane<br />frekvencije (heart rate recovery) - HRR.</p><p>Ispitivanje je obuhvatilo 90 ispitanika; 45<br />osoba mu&scaron;kog pola (20.4&plusmn;0.7 god., 184&plusmn;5.00<br />cm, 79.38&plusmn;9.42 kg, BMI 23.53&plusmn;2.83) i 45<br />osoba ženskog pola (20.5&plusmn;0.6 god., 168&plusmn;5.25<br />cm, 60.96&plusmn;6.93 kg, BMI 21.57&plusmn;2.23) -<br />studenata Univerziteta u Novom Sadu. Za<br />prikupljanje podataka kori&scaron;ćen je pulsmetar<br />(Polar, Finska). Ispitivanje je sprovedeno u<br />mirovanju, kao i u periodu oporavka posle<br />kratkotrajnog fizičkog opterećenja poznatog<br />intenziteta. U prvom modulu snimanje je<br />obavljano u miru, u sedećem poloţaju na<br />samom ergo-biciklu, stopala na platformi<br />ispred pedala, noge u fleksiji od 90&deg; u<br />kolenom zglobu, ruke na natkolenicama. U<br />drugom modulu snimanje je obavljeno u<br />priodu petominutnog oporavka posle<br />maksimalnog opteraćenja u trajanju od 30<br />sekundi (supramaksimalno opterećenje) -<br />Wingate protokol. U grupi mu&scaron;karaca<br />sprovedeno je jednokratno merenje, dok su za<br />grupu ţena isti moduli snimanja primenjeni u ri navrata: 1. U fazi menstrualnog krvarenja,<br />rana folikularna faza - najniži nivoi estrogena<br />i progesterona. 2. Kasna folikularna faza -<br />visok estrogen. 3. Srednja lutealna faza -<br />visok nivo progesterona i estrogena.<br />U miru kao i u poslednjem trominutnom<br />intervalu petominutnog oporavka određeni su<br />sledeći parametri varijabilnosti srčanog ritma:<br />srednja vrednost NN intervala - RRNN,<br />standardna devijacija NN intervala - SDNN,<br />kvadratni koren iz srednje vrednosti kvadrata<br />sukcesivnih razlika susednih NN intervala<br />(root mean square of successive differences) -<br />RMSSD, broj sucesivnih NN intervala koji<br />se razlikuju za vi&scaron;e od 50ms - NN50 i<br />procentualni udeo NN50 u ukupnom broju<br />NN intervala - pNN50. Od parametara<br />frekvencijskog domena, nakon brze Furijeove<br />transformacije analizirani su sledeći<br />parametri: snaga spektra niske frekvencije<br />(LF; 0,04-0,15Hz) i snaga spektra visoke<br />frekvencije (HF; 0,15-0,40Hz).<br />Oporavak srčane frekvencije u toku<br />petominutnog oporavka nakon<br />supramaksimalnog opterećenja na bicikl<br />ergometru procenjivan je pomoću sledećih parametara: 1. Apsolutna razlika između<br />vrednosti srčane frekvencije odmah po<br />zavr&scaron;etku opterećenja i frekvencije<br />registrovane nakon 60 sekundi oporavka -<br />HRR60. 2. Vremenska konstanta<br />kratkoročnog oporavka srčane frekvencije u<br />prvih 30 sekundi - T30. 3. Vremenska<br />konstanta opadanja srčane frekvencije u toku<br />petominutnog oporavka - T.<br />Utvrđeno je da mu&scaron;karci imaju veći pik snage<br />kao i prosečnu snagu pri supramaksimalnom<br />opterećenju u odnosu na grupu ţena bez<br />obzira na fazu menstrualnog ciklusa; dok su<br />bazalna i maksimalna srčana frekvencija bile<br />iste u obe grupe.<br />Postoje polne razlike u mehanizmima<br />vegetativne regulacije srčane frekvencije u<br />mirovanju. Najbolje su vidljive kroz<br />parametre frekvencijkog domena HRV-a (LF<br />i HF), odnosno prirodne logaritme ovih<br />vrednosti (lnLF i lnHF). Statistički značajne<br />razlike u vrednostima parametara<br />frekvencijskog domena HRV-a između grupe<br />mu&scaron;karaca i grupe ţena u sve tri faze<br />menstrualnog ciklusa potvrđene su i u fazi<br />oporavka posle supramaksimalnog opterećenja.<br />Postoje polne razlike u parasimpatičkoj<br />reaktivaciji posle supramaksimalnog<br />opterećenja koja je značajno brţa kod<br />mu&scaron;karaca. One se najbolje mogu proceniti<br />kroz matematičke modele oporavka srčane<br />frekvencije i vremensku konstantu opadanja<br />srčane frekvencije u prvih 30 sekundi<br />oporavka - T30.<br />Nisu utvrđene razlike u mehanizmima<br />vegetativne regulacije srčane frekvencije u<br />miru u grupi ţena po fazama menstrualnog<br />ciklusa; procenjeno kroz parametre<br />vremenskog i frekvencijskog domena HRVa.<br />Parametri vremenskog i frekvencijskog<br />domena HRV-a registrovani u mirovanju kao<br />i u fazi odmora posle supramaksimalnog<br />opterećenja nisu dovoljno osetljivi za<br />utvrđivanje razlika u vegetativnoj regulaciji<br />srčane frekvencije kod žena po fazama<br />menstrualnog ciklusa.<br />Nijedan od registrovanih parametara<br />oporavka srčane frekvencije (HRmax,<br />HRoporavak, HRR60, T i T30) nije se pokazao<br />dovoljno osetljivim za utvrđivanje promena u<br />parasimpetičkoj reaktivaciji kroz faze<br />menstrualnog ciklusa.</p>

<p>The aim of this study was to determine<br />gender differences in autonomic heart rate<br />control mechanisms, as well as to determine<br />heart rate control differences in women<br />during menstrual cycle. Heart rate variability<br />- HRV and heart rate recovery - HRR parameters were used.<br />The study included 90 participants; 45 males<br />(20.4&plusmn;0.7 yrs., 184&plusmn;5.00 cm, 79.38&plusmn;9.42 kg,<br />BMI 23.53&plusmn;2.83) and 45 females (20.5&plusmn;0.6<br />yrs., 168&plusmn;5.25 cm, 60.96&plusmn;6.93 kg, BMI<br />21.57&plusmn;2.23) - students of the University of<br />Novi Sad. Heart rate monitor (Polar,<br />Finland) was used for data collection.<br />Measurements were conducted while resting<br />as well as in a short recovery period after a<br />brief physical strain of known intensity. In<br />the first mode, heart rate monitoring was<br />conducted on relaxed subjects, in a sitting<br />position on an ergo-bike, feet on the<br />platform in front of the pedals, legs bent at<br />knees at 90&deg;, hands on thighs. In the second<br />mode heart rate monitoring was conducted in<br />a five-minute resting period after 30 seconds<br />of maximal exercise (supramaximal<br />exercise) - Wingate protocol. There was a<br />single monitoring in the male group, while in<br />the female group each monitoring mode was<br />conducted three times: 1. During the phase<br />of menstrual bleeding, early follicular phase<br />- the lowest levels of estrogen and<br />progesterone 2. Late follicular phase - high<br />estrogen. 3. Mid-luteal phase - high progesterone and estrogen.<br />While resting as well as in the last three<br />minutes of five-minute recovery period after<br />the exercise the following parameters of<br />heart rate variability were determined: the<br />mean value of NN intervals - RRNN, the<br />standard deviation of NN intervals - SDNN,<br />the square root of the mean of the squares of<br />the successive differences between adjacent<br />NN intervals (root mean square of<br />successive differences) - RMSSD, the<br />number of pairs of successive NN intervals<br />that differ by more than 50 ms - NN50 and<br />the proportion of NN50 divided by total<br />number of NN intervals pNN50. After the<br />fast Fourier transformation, following<br />frequency domain parameters were<br />analyzed: power spectrum of low frequency<br />(LF; 0,04-0,15Hz) and power spectrum of<br />high frequency (HF; 0,15-0,40Hz).<br />Heart rate recovery during the five-minute<br />resting period after the supramaximal<br />exercise on the ergo-bike was evaluated<br />through following parameters: 1. Absolute<br />difference between the heart rate<br />immediately after the exercise and the heart rate registered after 60 seconds of recovery -<br />HRR60. 2. Time constant of short-time heart<br />rate recovery in the first 30 seconds - T30. 3.<br />Time constant of heart rate decay<br />during the five-minute recovery period - T.<br />It was found that men had greater peak and<br />average power during supramaximal<br />exercise compared to a group of women<br />regardless of the phase of menstrual cycle;<br />while basal and maximal heart rate were the<br />same in both groups.<br />There are gender differences in autonomic<br />heart rate control mechanisms while resting.<br />These are best visible through frequency<br />domain HRV parameters (LF and HF), and<br />their natural logarithms (lnLF and lnHF).<br />Statistically significant differences in the<br />frequency domain HRV parameters between<br />the group of men and the group of women in<br />all three phases of the menstrual cycle, were<br />also found in recovery period after<br />supramaximal exercise.<br />There are gender differences in<br />parasympathetic reactivation after<br />supramaximal exercise which is significantly faster in men. These differences are best<br />assessed through mathematical models of<br />heart rate recovery and the time constant of<br />short-time heart rate recovery in the first 30<br />seconds - T30 .<br />No differences in autonomic heart rate<br />control mechanisms while resting in the<br />female group during three phases of<br />menstrual cycle were found; assessed<br />through the time and frequency domain<br />HRV parameters. The time and frequency<br />domain HRV parameters registered while<br />resting and during recovery period after<br />supramaximal еxеrcise were not sensitive<br />enough to determine differences in<br />autonomic heart rate control in women<br />through three phases of menstrual cycle.<br />None of the registered heart rate recovery<br />parameters (HRmax, HRR60, HRoporavak, T i<br />T30) were sensitive enough to determine<br />changes in parasympathetic reactivation<br />through a menstrual cycle.</p>