Med. & Biol. Eng. & Comput., 1978, 16, 383-386
Simple mechanical-chemical systemic pressure-control device S. S t a m a t e l o p o u l o s
A. Tsakiris
S. M o u l o p o u l o s Department of Clinical Therapeutics, Athens University Medical School,Athens, Greece Abstract--An implantable mechanical-chemical device was constructed to act as a feedback mechanism in controlling the blood pressure. It consisted of a balloon connected to a rubber catheter ending in a slit valve. Flow-pressure curves were derived from in v i t r o testings for three valve thresholds (120, 140 and 170 mmHg). Five fast-acting hypotensive drugs subsequently filled the device during 40 noradrenaline infusions in 25 dogs, with the balloon in the abdominal aorta and the catheter in the inferior vena cava. The results were as follows: (i) Following a short initial increase in systolic aortic pressure, significantly lower (p < 0. 001) than in control experiments, the device prevented any pressure rise above its threshold. (ii) The time needed for pressure lowering at the device's threshold depended on the drug used being 3 . 3 4 +_O 84 (mean + s.e. in minutes) for sodium nitroprusside, 5 . 9 9 + 0" 96 for phentolamin, 1 I . 63 +_2 . 9 7 for hydralazine, 14.52+-2.43 for a-methyl-dopa and 2 3 . 3 2 4 - 2 . 0 7 for diazoxide. K e y w o r d s - - A r t e r i a l hypertension, Pressure feedback
1 Introduction meter and a no. 16 rubber urethral catheter. The AN ATTEMPT to intervene, by means of electrical side-hole on this last catheter was occluded, and a devices, in the arterial pressure feedback mechanisms 1 mm long incision, parallel to the long axis of the of hypertensive subjects had been undertaken catheter, was made at this end. Balloon and catheters several years ago (GRIFFITH and SCHWARTZ, 1964; were filled with 0-9 % saline. External pressure, progressively increasing, was BILGUTAY and LILLEHEI, 1966; NEISTADT and SCHWARTZ, 1967). The devices used stimulated the carotid sinus nerves and successfully reduced the dortcl blood pressure in a number of cases (TUCKMAN et al., 1966; BREST, 1970). The method was, however, abandoned because of severe side-effects (HILAL and MASSUMI, 1966; FARREHIet al., 1969; ZESTet al., 1969). In the present work, a simple pressure regulating feedback mechanism was tested in the experimental animal. The purpose of the study was to investigate whether this implantable mechanical-chemical mechanism could prevent a rise in the animal's systolic blood pressure above its threshold. 2 Material and methods
2.1 Construction--in vitro testing The device was constructed as follows: A balloon 12cm in length and 1.5 cm in diameter (when inflated) and made of polyurethane, was attached to a polyethylene catheter (Fig. 1) marked at 5 mm distances. The length of the catheter was 30 cm and its internal diameter was 3 ram; the occluded end was inserted into the balloon after 14 side holes were made on it (1 mm diameter). The other end of the catheter was connected through a T-tube to a manoReceived 14th November 1977
C
T
Fig. 1 Experimentalset up : B air bubble in the transparent part of catheter M manometer T T-tube C clamp on the rubber catheter P Tr pressure transducer
0140-0118/78/0753-0000 $1.50/0 ~) IFMBE: 1978
Medical & Biological Engineering & Computing
July 1978
383
applied around the balloon and the indication of the manometer M, at which the saline was starting to flow through the incision-opening was noted. The incision was then made longer--if needed-- so that valves of thresholds 120, 140 and 170 mm Hg were selected for further testing. Valves with unstable thresholds were rejected. The rate of movement of an air bubble, in the polyethylene catheter, allowed flow measurement in the system during pressure increase. 2.2 Animal experiments Twenty-five dogs weighing from 21 to 29 kg were anaesthetised with Nembutal sodium (25 mg/kg of body weight). Following heparinisation (3 mg/kg) the balloon was introduced into the aorta, via the left femoral artery, and the rubber catheter was introduced into the inferior vena cava, (IVC) via the right femoral vein (Fig. 1). The polyethylene catheter remained outside the body to measure the flow as in Section 2.1. One of the following substances filled the rubber catheter before its introduction into the animah (i) sodium nitroprusside 12 mg/ml in nine animals (18 experiments), (ii) phentolamine 5 mg/ml in seven animals (11 experiments), (iii) hydralazine 25 m g / m l in three animals (three experiments), (iv) diazoxide 15 mg/ml in three animals (four experiments), (v) a-methyldopa 50 m g / m l in three animals (four experiments). The balloon was filled, after its introduction, with the same substance as the catheter. The aortic pressure was displayed on a Sanborn recorder through a catheter inserted via the right femoral artery. In all animals the aortic systolic pressure was below 170 mmHg before the beginning of the experiment. Following implantation of the device, an intravenous noradrenaline infusion (0.025 mg/min) was initiated under continuous pressure recording. The infusion was applied with the system functioning in 31 and clamped (clamp C, Fig. 1) in nine of the 40 experiments (in the 25 animals). These nine control experiments are included in the 18 experiments with sodium nitroprusside: The sequence of noradrenaline infusion with the device functioning or clamped was alternated in those 18 experiments. A minimum time period of 2 0 m i n was interposed between two subsequent experiments in the same animal. Only valves with 170 mmHg threshold were used in the experiments in vivo. 3 Results
3.1 In vitro testing Three distinct flow against pressure curves were obtained, one for each of the three thresholds. F o r pressure increases of up to 50 mmHg, above the corresponding threshold, flow was exponentially 384
increased with increasing pressure. At higher pressure the flow against pressure curve was linear. 3.2 In vivo testing Flow in the system initiated (Figs. 2 and 3) as soon as the systolic pressure rose above the threshold.
Fig. 2 Aortic pressure change from one dog, during noradrenaline infusion (upper trace). The rate of infusion of sodium nitroprusside is indicated in the lower panel (as measured from the rate of movement of the air bubble in the catheter). The initiation (,4) and the termination (B) of noradrenalin infusion are indicated by afro ws
Following an initial rise, systolic pressure oscillated around the threshold of the device. The flow ceased (Fig. 2) as soon as the pressure fell below the threshold, following noradrenaline discontinuation. Clamping of the device (Fig. 3) resulted in a marked increase in pressure, under the influence of the continuing noradrenaline infusion. The maximum systolic aortic pressure observed during the nine control experiments (280' 55 2 10.88 mmHg, mean + s.e.) was significantly higher
Fig. 3 Changes in aortic pressure (upper trace) and rate of sodium nitroprusside infusion through the system (lower trace) from one dog as in Fig. 2. The initiation of noradrenaline infusion is indicated by the black arrow. Following clamping of the system (white arrow) the aortic pressure rose under the influence of continuing noradrenaline infusion towards control values
Medical & Biological Engineering & Computing
July 1978
(t = 8-45, p < 0.001) than the corresponding value (186.77 + 2.12 mmHg) during functioning of the device in nine experiments with sodium nitroprusside. Tests with the remaining four drugs maintained, eventually, the systolic pressure around the threshold of the device. The mean time value (_+ s.e.) needed to lower the short initial pressure increase at the threshold level was: 3.34 + 0.84 min. for sodium nitroprusside, 5.99 + 0.96 rain. for phentolamine, 11"63 _+ 2.97 min. for hydralazine, 14.52 _+ 2.43 min. for a-methyl-dopa, and 23.32 + 2.07 min. for diazoxide.
for several pressure values, may be used to investigate further the characteristics of the regulatory mechanisms. The practical applicability, under certain modifications, may be envisioned for cases with frequent hypertensive paroxysms, until further measures, surgical or otherwise, can be taken to stabilise the pressure. References
BILGUTAY,A. M. and LILLEHEI, C. W. (1966) Surgical
treatment of hypertension with reference to baropacing. Amer. J. Cardiol. 17, 663-665. BREST, A. N. (1970) Carotio sinus nerves stimulation. 4 Discussion ibid. 26, 328-329. The need for automatic regulation of abnormal FARREHI,C., MEINZ, V. J., NEILL,W. A. and RITZMANN, L. W. (1969) The effects on stimulation of carotid variations in blood pressure is obvious. The results sinus nerves on coronary and systemic circulation. indicate that the device described functioned as an Circulation 40, 78. automatic regulator of abnormal pressure variations GOODMAN, L. S. and GILMAN, A. (1975) The pharmaproduced by noradrenaline infusion. The flow cological basis of therapeutics. Macmillan, London.714. against pressure relationship in the device allowed GRIFE1TH,L. S. J. and SCHWARTZ,S. J. (1964) Reversal of renal hypertension by electrical stimulation of more abrupt flow changes for higher pressure values carotid nerves. Surgery 56, 232-239. and less abrupt ones for pressure values around the GUYTON, A. C., COLEMAN, Z. G., COWLEY, A. W., threshold. SCHEEL, K. W. MANNING,R. D. and NORMAN,R. A. The time response (GuYTON et aL, 1974) of the (1974) in LARAGH,H. (Ed). Hypertension manuaL Dunfeedback system was very short. Of the concenDonneley, New York, 111-I 34. trations used, sodium nitroprusside produced the HILAL, H. and MASSUMI, R. (1966) Fatal ventricular fastest and diazoxide the slowest response to pressure fibrillation after carotid sinus stimulation. New EngL changes. This last finding is probably due to inJ. Med. 275, 157-160. activation of diazoxide (GooDMAN and GILMAN, NEISTADT, A. and SCHWARTZ, S. I. (1967) Effects of electrical stimulation of carotid sinus nerves in reversal 1975) since it was given by infusion and not as a of experimentally induced hypertension. Surgery bolus injection, Thus, the possibility arises that the 61, 932-961. device may be used experimentally in comparative pharmacological studies, where dosage-time res- TUCKMAN,J., REICH,W., TOODMAN,B., FRE1DMAN,E. and JACOnSON, J. H. (1966) Effects of radiofrequency ponse and length of action can be evaluated. carotid sinus nerve stimulation in patients with severe The study of the mosaic of regulatory mechanisms hypertension. Circulation 34, 231. affecting blood pressure could also be attempted by ZEFT, H. J., RUSKIN, J. and McCOWAN, R. K. (1969) the system described. The time relationship between Hypertension and carotid sinus nerve stimulation. pressure and respective flow changes in the system, New Engl. J. Med. 281, 103.
Un appareil chimio-mecanique simple de controle de pression systemique Sommaire---Un appareil chimio-m6canique d'implantation,a 6t6 construit pour fonctionnercommem6canisme de renvoi dans le contr61e de la pression sanguine. I1 se compose d'un ballon reli6 h u n cath6ter en caoutchouc, qui se termine par une soupape fendue. Les courbes de pression-d6bit proviennent d'essais in vitro, pour 3 seuils/t soupape (120, 140 et 170 mmHg). Cinq m6dicaments hypotensifs, d'action rapide, remplissent par la suite l'appareil, lors de 40 infusions de noradr6natine, dans 25 chiens; le ballon 6tant dans l'aorte abdominale, et le cath6ter dans la veine cave inf6rieure. Les r6sultats sont les suivants: (i) Faisant suite h une courte augmentation initiale de la pression aortique systolique, relativement plus faihle (p < 0-00l) que celle des exp6riences de contr61e, l'appareil emp&he toute mont6e de pression au-dessus de son scull. (ii) Le temps n6cessaire ~t la descente de pression, au seuil de l'appareil, d6pend du m6dicament utilis6, soit: 3" 34 _+ 0" 84 (moyenne_+s.e., par minute) de nitroprusside de sodium, 5' 99 + 0.96 de phentolamine, 11" 63 + 2" 97 d'hydralazine, 14" 52 + 2' 43 de m6thyl6ne-dopa et 23" 32 + 2" 07 d'oxyde diazoique. Medical & Biological Engineering & Computing E
July 1978
385
Ein einfacher mechanisch-chemischer innertherapeutischer Druckregler Zusammenfassung--Es wurde ein einpflanzbarer, mechanisch-chemischer Druckregler konstruiert, der bei der Reglung des Blutdrucks als Rtickfiihrmechanismus arbeitet. Er bestand aus einem Ballon, der an ein Gumrnikatheter angeschlossen war, das am Ende zu einem Schlitzventil geformt war. M a n erhielt FluBdruckkurven aus in vitro Prtifungen von den Schwellenwerten dreier Ventile (120, 140 und 170 mmHg). Ftinf schnellwirkende, blutdrucksenkende Medikamente ftillten wahrend 40 Noradrenaline-Infusionen bei 25 Hunden das Ger/it, wobei tier Ballon an die abdominale Aorta und das Katheder in die weiter unten liegende Vena Cava angeschlossen waren. Die Resultate waren wie folgt: (i) Einer kurzen, anf~inglichen Steigerung des systolisch aortischen Drucks zufolge, der bedeutend (p < 0,001) niedriger als bei den Reglerexperimenten war, verhinderte das Ger~tt jeglichen Druckanstieg fiber den Schwellenwert hinaus. (ii) Die fiJr die Drucksenkung am Schwellenwert des Get/ires benbtigte Zeit hing yon dem verwendeten Medikament ab und war 3,34 + 0,84 (Durchschnitt + s.e., in rain) fiir Sodiumnitroprussid, 5,99 + 0,96 fiir Phentolamin, 11,63 + 2,97 ftir Hydrazalin, 14,52 _ 2,43 ftir a-Methyl-Dopa und 23,32 + 2,07 fiir Diazoxyd.
386
Medical & Biological Engineering & Computing
July 1978
Simple mechanical-chemical systemic pressure-control device S. S t a m a t e l o p o u l o s
A. Tsakiris
S. M o u l o p o u l o s Department of Clinical Therapeutics, Athens University Medical School,Athens, Greece Abstract--An implantable mechanical-chemical device was constructed to act as a feedback mechanism in controlling the blood pressure. It consisted of a balloon connected to a rubber catheter ending in a slit valve. Flow-pressure curves were derived from in v i t r o testings for three valve thresholds (120, 140 and 170 mmHg). Five fast-acting hypotensive drugs subsequently filled the device during 40 noradrenaline infusions in 25 dogs, with the balloon in the abdominal aorta and the catheter in the inferior vena cava. The results were as follows: (i) Following a short initial increase in systolic aortic pressure, significantly lower (p < 0. 001) than in control experiments, the device prevented any pressure rise above its threshold. (ii) The time needed for pressure lowering at the device's threshold depended on the drug used being 3 . 3 4 +_O 84 (mean + s.e. in minutes) for sodium nitroprusside, 5 . 9 9 + 0" 96 for phentolamin, 1 I . 63 +_2 . 9 7 for hydralazine, 14.52+-2.43 for a-methyl-dopa and 2 3 . 3 2 4 - 2 . 0 7 for diazoxide. K e y w o r d s - - A r t e r i a l hypertension, Pressure feedback
1 Introduction meter and a no. 16 rubber urethral catheter. The AN ATTEMPT to intervene, by means of electrical side-hole on this last catheter was occluded, and a devices, in the arterial pressure feedback mechanisms 1 mm long incision, parallel to the long axis of the of hypertensive subjects had been undertaken catheter, was made at this end. Balloon and catheters several years ago (GRIFFITH and SCHWARTZ, 1964; were filled with 0-9 % saline. External pressure, progressively increasing, was BILGUTAY and LILLEHEI, 1966; NEISTADT and SCHWARTZ, 1967). The devices used stimulated the carotid sinus nerves and successfully reduced the dortcl blood pressure in a number of cases (TUCKMAN et al., 1966; BREST, 1970). The method was, however, abandoned because of severe side-effects (HILAL and MASSUMI, 1966; FARREHIet al., 1969; ZESTet al., 1969). In the present work, a simple pressure regulating feedback mechanism was tested in the experimental animal. The purpose of the study was to investigate whether this implantable mechanical-chemical mechanism could prevent a rise in the animal's systolic blood pressure above its threshold. 2 Material and methods
2.1 Construction--in vitro testing The device was constructed as follows: A balloon 12cm in length and 1.5 cm in diameter (when inflated) and made of polyurethane, was attached to a polyethylene catheter (Fig. 1) marked at 5 mm distances. The length of the catheter was 30 cm and its internal diameter was 3 ram; the occluded end was inserted into the balloon after 14 side holes were made on it (1 mm diameter). The other end of the catheter was connected through a T-tube to a manoReceived 14th November 1977
C
T
Fig. 1 Experimentalset up : B air bubble in the transparent part of catheter M manometer T T-tube C clamp on the rubber catheter P Tr pressure transducer
0140-0118/78/0753-0000 $1.50/0 ~) IFMBE: 1978
Medical & Biological Engineering & Computing
July 1978
383
applied around the balloon and the indication of the manometer M, at which the saline was starting to flow through the incision-opening was noted. The incision was then made longer--if needed-- so that valves of thresholds 120, 140 and 170 mm Hg were selected for further testing. Valves with unstable thresholds were rejected. The rate of movement of an air bubble, in the polyethylene catheter, allowed flow measurement in the system during pressure increase. 2.2 Animal experiments Twenty-five dogs weighing from 21 to 29 kg were anaesthetised with Nembutal sodium (25 mg/kg of body weight). Following heparinisation (3 mg/kg) the balloon was introduced into the aorta, via the left femoral artery, and the rubber catheter was introduced into the inferior vena cava, (IVC) via the right femoral vein (Fig. 1). The polyethylene catheter remained outside the body to measure the flow as in Section 2.1. One of the following substances filled the rubber catheter before its introduction into the animah (i) sodium nitroprusside 12 mg/ml in nine animals (18 experiments), (ii) phentolamine 5 mg/ml in seven animals (11 experiments), (iii) hydralazine 25 m g / m l in three animals (three experiments), (iv) diazoxide 15 mg/ml in three animals (four experiments), (v) a-methyldopa 50 m g / m l in three animals (four experiments). The balloon was filled, after its introduction, with the same substance as the catheter. The aortic pressure was displayed on a Sanborn recorder through a catheter inserted via the right femoral artery. In all animals the aortic systolic pressure was below 170 mmHg before the beginning of the experiment. Following implantation of the device, an intravenous noradrenaline infusion (0.025 mg/min) was initiated under continuous pressure recording. The infusion was applied with the system functioning in 31 and clamped (clamp C, Fig. 1) in nine of the 40 experiments (in the 25 animals). These nine control experiments are included in the 18 experiments with sodium nitroprusside: The sequence of noradrenaline infusion with the device functioning or clamped was alternated in those 18 experiments. A minimum time period of 2 0 m i n was interposed between two subsequent experiments in the same animal. Only valves with 170 mmHg threshold were used in the experiments in vivo. 3 Results
3.1 In vitro testing Three distinct flow against pressure curves were obtained, one for each of the three thresholds. F o r pressure increases of up to 50 mmHg, above the corresponding threshold, flow was exponentially 384
increased with increasing pressure. At higher pressure the flow against pressure curve was linear. 3.2 In vivo testing Flow in the system initiated (Figs. 2 and 3) as soon as the systolic pressure rose above the threshold.
Fig. 2 Aortic pressure change from one dog, during noradrenaline infusion (upper trace). The rate of infusion of sodium nitroprusside is indicated in the lower panel (as measured from the rate of movement of the air bubble in the catheter). The initiation (,4) and the termination (B) of noradrenalin infusion are indicated by afro ws
Following an initial rise, systolic pressure oscillated around the threshold of the device. The flow ceased (Fig. 2) as soon as the pressure fell below the threshold, following noradrenaline discontinuation. Clamping of the device (Fig. 3) resulted in a marked increase in pressure, under the influence of the continuing noradrenaline infusion. The maximum systolic aortic pressure observed during the nine control experiments (280' 55 2 10.88 mmHg, mean + s.e.) was significantly higher
Fig. 3 Changes in aortic pressure (upper trace) and rate of sodium nitroprusside infusion through the system (lower trace) from one dog as in Fig. 2. The initiation of noradrenaline infusion is indicated by the black arrow. Following clamping of the system (white arrow) the aortic pressure rose under the influence of continuing noradrenaline infusion towards control values
Medical & Biological Engineering & Computing
July 1978
(t = 8-45, p < 0.001) than the corresponding value (186.77 + 2.12 mmHg) during functioning of the device in nine experiments with sodium nitroprusside. Tests with the remaining four drugs maintained, eventually, the systolic pressure around the threshold of the device. The mean time value (_+ s.e.) needed to lower the short initial pressure increase at the threshold level was: 3.34 + 0.84 min. for sodium nitroprusside, 5.99 + 0.96 rain. for phentolamine, 11"63 _+ 2.97 min. for hydralazine, 14.52 _+ 2.43 min. for a-methyl-dopa, and 23.32 + 2.07 min. for diazoxide.
for several pressure values, may be used to investigate further the characteristics of the regulatory mechanisms. The practical applicability, under certain modifications, may be envisioned for cases with frequent hypertensive paroxysms, until further measures, surgical or otherwise, can be taken to stabilise the pressure. References
BILGUTAY,A. M. and LILLEHEI, C. W. (1966) Surgical
treatment of hypertension with reference to baropacing. Amer. J. Cardiol. 17, 663-665. BREST, A. N. (1970) Carotio sinus nerves stimulation. 4 Discussion ibid. 26, 328-329. The need for automatic regulation of abnormal FARREHI,C., MEINZ, V. J., NEILL,W. A. and RITZMANN, L. W. (1969) The effects on stimulation of carotid variations in blood pressure is obvious. The results sinus nerves on coronary and systemic circulation. indicate that the device described functioned as an Circulation 40, 78. automatic regulator of abnormal pressure variations GOODMAN, L. S. and GILMAN, A. (1975) The pharmaproduced by noradrenaline infusion. The flow cological basis of therapeutics. Macmillan, London.714. against pressure relationship in the device allowed GRIFE1TH,L. S. J. and SCHWARTZ,S. J. (1964) Reversal of renal hypertension by electrical stimulation of more abrupt flow changes for higher pressure values carotid nerves. Surgery 56, 232-239. and less abrupt ones for pressure values around the GUYTON, A. C., COLEMAN, Z. G., COWLEY, A. W., threshold. SCHEEL, K. W. MANNING,R. D. and NORMAN,R. A. The time response (GuYTON et aL, 1974) of the (1974) in LARAGH,H. (Ed). Hypertension manuaL Dunfeedback system was very short. Of the concenDonneley, New York, 111-I 34. trations used, sodium nitroprusside produced the HILAL, H. and MASSUMI, R. (1966) Fatal ventricular fastest and diazoxide the slowest response to pressure fibrillation after carotid sinus stimulation. New EngL changes. This last finding is probably due to inJ. Med. 275, 157-160. activation of diazoxide (GooDMAN and GILMAN, NEISTADT, A. and SCHWARTZ, S. I. (1967) Effects of electrical stimulation of carotid sinus nerves in reversal 1975) since it was given by infusion and not as a of experimentally induced hypertension. Surgery bolus injection, Thus, the possibility arises that the 61, 932-961. device may be used experimentally in comparative pharmacological studies, where dosage-time res- TUCKMAN,J., REICH,W., TOODMAN,B., FRE1DMAN,E. and JACOnSON, J. H. (1966) Effects of radiofrequency ponse and length of action can be evaluated. carotid sinus nerve stimulation in patients with severe The study of the mosaic of regulatory mechanisms hypertension. Circulation 34, 231. affecting blood pressure could also be attempted by ZEFT, H. J., RUSKIN, J. and McCOWAN, R. K. (1969) the system described. The time relationship between Hypertension and carotid sinus nerve stimulation. pressure and respective flow changes in the system, New Engl. J. Med. 281, 103.
Un appareil chimio-mecanique simple de controle de pression systemique Sommaire---Un appareil chimio-m6canique d'implantation,a 6t6 construit pour fonctionnercommem6canisme de renvoi dans le contr61e de la pression sanguine. I1 se compose d'un ballon reli6 h u n cath6ter en caoutchouc, qui se termine par une soupape fendue. Les courbes de pression-d6bit proviennent d'essais in vitro, pour 3 seuils/t soupape (120, 140 et 170 mmHg). Cinq m6dicaments hypotensifs, d'action rapide, remplissent par la suite l'appareil, lors de 40 infusions de noradr6natine, dans 25 chiens; le ballon 6tant dans l'aorte abdominale, et le cath6ter dans la veine cave inf6rieure. Les r6sultats sont les suivants: (i) Faisant suite h une courte augmentation initiale de la pression aortique systolique, relativement plus faihle (p < 0-00l) que celle des exp6riences de contr61e, l'appareil emp&he toute mont6e de pression au-dessus de son scull. (ii) Le temps n6cessaire ~t la descente de pression, au seuil de l'appareil, d6pend du m6dicament utilis6, soit: 3" 34 _+ 0" 84 (moyenne_+s.e., par minute) de nitroprusside de sodium, 5' 99 + 0.96 de phentolamine, 11" 63 + 2" 97 d'hydralazine, 14" 52 + 2' 43 de m6thyl6ne-dopa et 23" 32 + 2" 07 d'oxyde diazoique. Medical & Biological Engineering & Computing E
July 1978
385
Ein einfacher mechanisch-chemischer innertherapeutischer Druckregler Zusammenfassung--Es wurde ein einpflanzbarer, mechanisch-chemischer Druckregler konstruiert, der bei der Reglung des Blutdrucks als Rtickfiihrmechanismus arbeitet. Er bestand aus einem Ballon, der an ein Gumrnikatheter angeschlossen war, das am Ende zu einem Schlitzventil geformt war. M a n erhielt FluBdruckkurven aus in vitro Prtifungen von den Schwellenwerten dreier Ventile (120, 140 und 170 mmHg). Ftinf schnellwirkende, blutdrucksenkende Medikamente ftillten wahrend 40 Noradrenaline-Infusionen bei 25 Hunden das Ger/it, wobei tier Ballon an die abdominale Aorta und das Katheder in die weiter unten liegende Vena Cava angeschlossen waren. Die Resultate waren wie folgt: (i) Einer kurzen, anf~inglichen Steigerung des systolisch aortischen Drucks zufolge, der bedeutend (p < 0,001) niedriger als bei den Reglerexperimenten war, verhinderte das Ger~tt jeglichen Druckanstieg fiber den Schwellenwert hinaus. (ii) Die fiJr die Drucksenkung am Schwellenwert des Get/ires benbtigte Zeit hing yon dem verwendeten Medikament ab und war 3,34 + 0,84 (Durchschnitt + s.e., in rain) fiir Sodiumnitroprussid, 5,99 + 0,96 fiir Phentolamin, 11,63 + 2,97 ftir Hydrazalin, 14,52 _ 2,43 ftir a-Methyl-Dopa und 23,32 + 2,07 fiir Diazoxyd.
386
Medical & Biological Engineering & Computing
July 1978
