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Kokyu to Junkan Volume 33, Issue 5 （May 1985）

呼吸と循環 33巻5号（1985年5月発行）

Japanese English

研究

低酸素心拍数応答に及ぼす加齢，遺伝の影響—双生児法による研究 The effects of aging and genetic factors on heart rate response to hypoxia: Studies in twins 宮本顕二 ¹ , 吉川隆志 ^1,2 , 山本宏司 ¹ , 西浦洋一 ¹ , 鈴木章彦 ¹ , 西村正治 ¹ , 志田晃 ^1,3 , 岸不尽弥 ¹ , 川上義和 ¹ Kenji Miyamoto ¹ , Takashi Yoshikawa ^1,2 , Hiroshi Yamamoto ¹ , Yohichi Nishiura ¹ , Akihiko Suzuki ¹ , Akira Shida ^1,3 , Fujiya Kishi ¹ , Yoshikazu Kawakami ¹ ¹北海道大学医学部第一内科 ²帯広厚生病院内科 ³国立函館病院内科 ¹The First Department of Medicine, School of Medicine, Hokkaido University ²The Department of Medicine, Obihiro Kosei Hospital ³The Department of Medicine, Hakodate National Hospital pp.669-677

発行日 1985年5月15日 Published Date 1985/5/15

DOI https://doi.org/10.11477/mf.1404204675

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Abstract 文献概要
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　生体において，年齢，性，体格などを標準化してもなお血圧，心拍数に個人差のある事は良く知られた事実である。一方，双生児研究により，安静時血圧，心拍数，心電図P-Q間隔が一卵性双生児で二卵性双生児より似ている事実が報告され，あるいは，本態性高血圧症は家族内発症が高く，一卵性双生児の一方が高血圧症の場合，他方も高血圧症である確率が高い。また，一卵性双生児で血圧の日内変動がよく似ている事実^1）なども明らかにされてきた。以上の事実から血圧を含む循環調節機構に遺伝子因子が関与している事が推測される。

　本研究は若年から老年に至る男女双生児を対象に，動脈血ガス二重制御システム^2）を用い，吸入酸素濃度を徐徐に低下させ，低酸素血症を誘導した。そして，その過程の心拍数変化を求め，低酸素循環調節機構に及ぼす遺伝の影響を検討した。また，健常成人男子を対象に肺・胸郭系の動きが心拍数に及ぼす影響を化学因子から分離評価することを試みた。

We studied the role of genetics and environmental factors determining heart rate response to isocap-nic hypoxia (study-1), and the effect of pulmonary inflation reflex, which is activated by the increases in ventilation induced by chemoreceptor stimulation (study-2).

Study-1 51 pairs of twins (34 MZ and 17 DZ) of both sexes, ranging in age from 15 to 58 years, were used as subjects. Heart rate response (4HR/dSa_O2) was determined by a dual control system developed to automatically attain isocapnic hypoxia. Hy-poxic ventilatory response (A) was also determined. The variable ΔHR/ΔSa_O2 was assessed by the lin-ear equation ; HR=HRo+ΔHR/ΔSa_O2 (100-Sa_O2), The range of ΔHR/ΔSa_O2 was 0.257-2.223 (mean ±SD=1.011±0.493) beats/min/1% fall in Sa_O2. Heart rate response to hypoxia diminishes with age (r=-0.540 p<0.05). There is no relationship between ΔHR/ΔSa.02 and body size. To evaluate genetic factors that have effect on the heart rate response to hypoxia, we separated the twins into two groups, young twin group and adult twin group. Young twin group (15-18 yrs) consisted of high school students who were living together in the same family since their birth. Adult twin group (26-58yrs) consisted of twins who were living separately because of marriage, employment or other reasons. In the young twin group, intrapair variance for ΔHR/ΔSa₀₂ was sig-nificantly smaller in MZ than in DZ. In the adult twin group, intrapair variance was not significant between MZ and DZ.

Study-2 Six healthy male subjects (aged 21-31 yrs) entered this study to evaluate the effect of pul-monary inflation reflex during progressive isocapnic hypoxia. The subjects were allowed to breathe spon-taneously during hypoxia (free-breathing test). After 10 minute's rest, they maintained the pre-test levelof ventilation by watching an occiloscope screen dis-playing a tidal volume and by listening to the sound of a metronome during progressive hypoxia (control-led-breathing test).

In both tests, we determined ΔHR/ΔSa_O2. ΔHR/ΔSa_O2 of free-breathing test is 0.841±0.254 (mean ±SD) beats/min/1% fall in Sa_O2. ΔHR/ΔSa_O2 of controlled-breathing test is 0.716±0.199. There was on significant difference in heart rate response between the tests.

These results suggest : 1) Heart rate response to hypoxia diminishes with age and is not related to body size. 2) Heart rate response to hypoxia is, at least partially, under the influence of genetic factors. 3) The occurance of tachy-cardia during progressive hypoxia does not depend on the ventilatory response to chemoreceptor stimula-tion.