Inter-machine variability in the stability of continuous positive airway pressure

Transcription

1 Eur Resplr J 1992, 6, TECHNICAL NOTE Inter-mchine vribility in the stbility of continuous positive irwy pressure M. Jckson, M.A. King, J.M. Shneerson Inter-mchine vribility in the stbility of continuous positive irwy pressure. M. Jckson, M.A. King, J.M. Shneerson. ABSTRACT: Two studies were performed to Investigte the differences In pressure stbility performnce of the continuous positive irwy pressure (CPAP) mchines used by our ptients. The vritions of msk pressures during ech respirtory cycle were mesured during overnight studies of two groups of ptients with obstructive sleep pnoe, who were using either Sleep-Esy Ill CPAP mchine or SI-Pln CPAP unit. The ptients were well-mtched for ge, weight nd neck circumference. The group using the SI-Pln unit hd more constnt msk pressures nd were using lower CPAP pressures (men 1.6 cmh 1 ) thn those using the Sleep-Esy lii,mchine (men 13.8 cmh 1 ) (p<o.oz). The pressure stbility performnce of five CPAP mchines used by our ptients ws lso compred using stndrdized simulted ptient breths pro duced by negtive pressure cuirss pump. There were lrge differences between the mchines In bility to mintin constnt pressure. Using tidl volume of. I nd pek now rtes of between Z-4 l mjn 1 the pressure vrition rnged from -67% of the minimum Inspirtory pressure. The mintennce of constnt pressure during Inspirtion nd expirtion lowers the men pressure required to eliminte obstructive sleep pnoes nd reduces the likelihood of pressure relted side-effects. Eur Respir J., 1992,, The Assisted Ventiltion Unit Ppworth Hospitl Ppworth Everrd Cmbridge UK Correspondence: M. Jckson The Asisted Ventiltion Unit Ppworth Hospitl Ppworth Everrd Cmbridge CB3 8RE UK Keywords: Continuous positive irwy pressure obstructive sleep pnoe Received: October Accepted fter revision Jnury M.J. is supported by the British Scoliosis Reserch Foundtion. Obstructive sleep pnoe is common nd more frequently recognized condition with prevlence of up to 1% in men of working ge. Since its introduction in 1981 [1), the effectiveness of nsl continuous positive irwy pressure (CPAP) hs become well estblished nd lrge number of CP AP mchines re now in use. Our own unit first offered CPAP tretment in 1986 nd now hs over 9 ptients with mchines t home. When inititing CP AP it is usul to determine the minimum pressure tht is effective in order to reduce the incidence of pressure relted side-effects. This pressure is determined during n overnight study by grdully incresing the msk pressure until episodes of irwy obstruction re bolished. We hve observed wide vritions in the mesured msk pressure, both within respirtory cycles nd with different CP AP mchines. We hve performed two studies in order to investigte the mgnitude of these pressure vritions. In the first study, we mesured the vrition in msk pressure during ech respirtory cycle in ptients treted with two different CPAP mchines. In the second study, we tested the stbility of pressure delivered by five different CP AP mchines which re in use by our ptients by using series of stndrd reproducible simulted ptient breths. Ptient study Methods Twenty mle ptients (men ge 6 yrs) were studied. Ten used the Sleep-Esy Ill CPAP mchine with the Snders circuit (Respironics Inc., Monroeville, USA) nd ten were using the Si-Pln unit (Si-Pln Electronics Reserch Ltd, Strtford upon Avon, UK), using msk with 4 mm blow-hole. Ech group of 1 were consecutive dmissions of ptients using the two mchines. The ptients were well-mtched for ge, weight nd neck circumference (tbles 1 nd 2). The ptients using the Sleep-Esy Ill mchine hd been treted with CP AP for longer time, reflecting the reltively recent introduction of the Si-Pln unit. Oxygen sturtion (Ohmed Biox 37 pulse oximeter) nd msk pressure were continully mesured throughout n overnight study using clibrted - cmh 2 pressure trnsducer (Si-Pln Electronics Reserch Ltd). The pressure ws recorded on therml rry recorder (Astr-Med Dsh 2 recorder) t chrt speed of 1 mm min' 1 to llow mesurement of chnges of pressure during individul breths. The men mximum nd minimum msk pressures were clculted from mesurement over consecutive

2 88 M. JACKSON, M.A. KING, J.M. SHNEBRSON breths t three seprte periods during the study. The periods were selected to be t times when the ptients were observed to be sleep nd oxygen sturtion nd msk pressure recordings stble. The chnges in msk pressure were clculted s percentge of both the minimum nd mximum msk pressures. Flow nd volume were mesured using pneumotchogrph (P.K. Morgn Ltd). Pressure ws mesured using clibrted -2 cmhzo pressure trnsducer (Si-Pln Electronics Reserch Ltd). Ail signls were recorded on computer-bsed dt logger nd hrd copies mde on plotter (fig. 1). Mchine study Five CP AP mchines were studied. They were the Respironics Sleep-Esy Ill, Sefm Pression, Puritn Bennett 1, Helthdyne 9 nd the Si-Pln CPAP unit. An inspirtory effort ws simulted using negtive pressure cuirss pump (Newmrket Pump, Si-pln Electronics Reserch Ltd), to produce pek flow rtes of 2-6 l min 1 nd cycle volumes of.,.7 nd 1 I. The pressure wveform ws hlf sine wve. Tble 1. - Detils of ptients using the SI-Pln CPAP unit Pt. no Men SD Age Time on yrs CPAP months Wt kg Ht Neck Occ. hose cm circ. pressure cm cmhp CPAP: continuous positive irwy pressure; circ.: circumference; Pt.: ptient; Occ.: occluded. Tble 2. - mchine Pt. no Men 6 SD 13.1 Detils of ptients using Sleep-Esy Ill Age Time on Wt yrs CPAP kg months Ht cm Neck Occ. hose circ. pressure cm cmhp CPAP: continuous positive irwy pressure; circ.: circumference; Pt.: ptient; Occ.: occluded. Flow 'Ptient' CPAP pressure pump pressure Dt logger CPAP test circu Fig Circuit digrm of the mchine study. CPAP: continu ous positive irwy pressure mchine: VDU: visul disply unit. The CPAP mchines were ech set t, 1 nd 1 cmhp with the set pressure being tht recorded t the ptient end of. the hose with tht end occluded. The chnge of pressure t the ptient end of the hose ws mesured during the simulted inspirtory efforts. A similr comprison ws mde with the mchines set t 1 cmh nd with the cuirss pump pressure delivered s full sine wve simulting inspirtion nd expirtion producing pek flow rte of 4 l min 1. The differences between occluded pressures used by the ptients nd the overnight msk pressure vritions were nlysed using the two smple t-test, tking p<. to indicte significnt difference. Ptient study Results The ptients treted using the Si-Pln unit tended to use lower CPAP pressures (men 1.6 cmhp, so 3.8) compred with those using the Sleep-Esy mchine (men 13.8 cmh 2, so 2.62 cmhp) (p<.2). During sleep the msk pressures vried between.-1. cmh 2 (men.96 cmh_p) in the Si Pln group nd between cmh u (men 2.68 cmhp) in the Sleep-Esy group (p<o.ool ). As percentges of the minimum (inspirtory) pressure this ws equivlent to fll of pressure of between % in the group using the Sleep-Esy III mchine nd between % in the group using the Si-Pln unit. Similrly s percentge of the mximum (expirtory) level the pressure flls represented between % in the Sleep-Esy group nd between % in the Si-Pln group. The individul pressure vritions in the two groups re shown in figure 2 nd the percentge flls of pressure in reltion to the mximum nd minimum msk pressures re shown in figure 3 nd b.

3 INTER-MACHINE VARIABIUTY IN STABILITY OF CPAP 89 f 1s --H-oltn-ll -li--- r o ll... B -.. ::r:c\1 E Ptients using Sleep-Esy Ill 2or _... -fj... i » C D...-[j'"_"_' '"'"'fi"""'"''' ''' """""""' D Ptients using Si-Pln Fig Individul msk pressure vritions in the two groups of ptients. CP AP: continuous positive irwy pressure. 2 ::r:c\1 e [.. b % fll of CPAP pressure OC\1 ::r: 1!:! % fll of CPAP pressure Fig ) Flls of msk pressure s percentge of the mximum msk pressure...._ : Si-Pln; - : Sleep-Esy. b) Flls of msk pressure s percentge of the minimum msk pres sure.--+- :Si-Pln ;-: Sleep-Esy. CPAP: continuous positive irwy pressure. Mchine study There ws little intr-mchine vribility on repeted testing t individul settings of flow, volume nd set pressure. There were, however, considerble differences between the performnce of the five mchines. When the CP AP mchines were subjected to simulted inspirtion of. 1 t pek flow rtes of min 1 the flls of pressure vried between -67% of the lowest (''inspirtory") pressure. The lrger flls were recorded with the combintion of lower set pressures nd higher ''inspirtory" flow rtes (fig. 4). At higher flow rtes of nd 6 1 min 1 nd tidl volume of.7 1 the sme trend ws observed, with flls of delivered pressure of between 2.7-9% of the inspirtory level. The Si-Pln unit performed best t ll combintions of tidl volume nd inspirtory flow !!! ::l 4-3 J!! 2 1 ol-----==== Flow I min 1 b !!! 6 ::l 4 3 J!!,2 1 ol Flow l mln :! c ol = Flow I min 1 Fig Mchine study: flls of pressure expressed s percentge of the minimum pressure when subjected to simulted ispi rtion of O.S I t flow rtes of 2, 3 nd 4 / mi. CPAP pressure set t: ) S cmh 3 ; b) 1 cmhp; c) 1 cmfi,o.-- : Si-Pln; -.o+-: Sleep-Esy Ill;- : Puritn Bennett SlS;-: Heltbdyne;- : Sefm.

4 9 M. JACKSON, M.A. KING, J.M. SHNEERSON n i tl "' Q u.. g_... _ () , ! o Puritn Sefm Helthdyne Sleep-Esy SI-Pln Bennett 1 Ill Fig.. - Mchine study: CPAP vrition in response to simultion of full respirtory cycle. Sine pressure wve form CPAP set t 1 cmh,q. Flow 4 l min. TV. I. CPAP: continuous positive irwy pressure; TV: tidl volume. The full respirtory cycle simultion, with tidl volume of. I nd pek flow rte of 4 l min 1 t set pressure of 1 cmh_z..o resulted in pressure flls of between.2-3. cmhp during the inspirtory phse nd n expirtory o:vershoot of between -2 cmhp with the different mchines (fig. ). Discussion The mechnism of ction of CP AP hs been the subject of number of studies. Some hve suggested tht the mintennce of upper irwy ptency is medited by lung infltion with rised functionl residul cpcity (FRC) [2-4]. It is, however, more likely!'ht CP AP works primrily s pneumtic splint [, 6], with the rised intrluminl pressure opposing the forces tending to collpse the irwy. The timing of irwy closure during sleep pnoes hs been investigted, with some uthors relting it to the negtive intrluminl pressures generted on inspirtion [7-9] nd others to the nrrowing of the irwy tht occurs on expirtion [1, 11]. It is likely tht both fctors re importnt, with nrrowed irwy t end expirtion completely closing when negtive pressure develops t the onset of inspirtion. Obstructive sleep pnoe occurs most commonly in obese individuls, probbly becuse of mss loding of the collpsible portion of their upper irwys [12-14], which increses the likelihood of irwy nrrowing on expirtion. The importnce of the timing of the ppliction of the positive pressure during the respirtory cycle hs recently been investigted. Although positive irwy pressure is conventionlly delivered during both inspirtion nd expirtion, studies using mchine in which the inspirtory nd expirtory irwy pressure could be independently djusted (Bi-PAP) showed tht lower level of expirtory positive irwy pressure (EP AP) ws required when delivered with n inspirtory positive irwy pressure (IP AP) which is no different to the effective CP AP pressure [1]. The ptient's inspirtory effort drws ir from the CPAP circuit nd tends to lower the pressure. The minimum pressure during inspirtion is conventionlly tken s the CP AP pressure. Most CP AP mchines mintin this minimum inspirtory pressure t the expense of expirtory pressures tht re higher thn required. During expirtion, the exhled gs from the ptient is dded to the CP AP system nd the pressure rises unless it is controlled by rpidly responding servo-system. The idel mchine would mintin the criticl (minimum) inspirtory pressure throughout inspirtion with little rise in expirtory pressure. The mchine study hs shown tht there is gret vrition in the bility of the different CP AP mchines to mintin constnt pressure level. If the level of the minimum inspirtory pressure is the criticl determinnt of irwy stbility then the pek to trough difference is the pressure unnecessrily delivered during expirtion. Our study hs shown tht considerble pressure my be unnecessrily delivered during expirtion by some mchines but tht this cn be clerly reduced under comprble conditions of flow nd volume by using mchine with good mintennce of inspirtory pressure. The ptient study hs shown tht the msk pressure vries by s much s 34% of the minimum msk pressure with conventionl mchines. This vribility cn be considerbly reduced by using mchine such s the Si-Pln unit, which llowed, t most, fll of only 12% of the minimum msk pressure. The clinicl importnce of using mchine with well-mintined inspirtory pressure is tht it reduces the men CP AP pressure required to chieve upper irwy stbility nd bolish the obstructive pnoes. This is reflected in the ptient study by the lower CPAP pressures required in ptients using the Si-Pln CP AP unit. The use of mchines which will deliver the minimum required inspirtory pressure in this wy will reduce the dverse effects of high pressure such s middle er symptoms, gstric distension nd ir leks

5 INTER MACHINE VARIABILITY IN STABIUTY OF CPAP 91 which my cuse conjunctivl irrittion []. A lower pek msk pressure my lso llow looser djustment of the CPAP msk nd reduce the likelihood of pressure sores. References 1. Sullivn CE, Iss PG, Berthon-Iones M, Eves L. - Reversl of obstructive sleep pne by CP AP pplied through the nres. Lncet, 1981; i: Brown I, Tylor R, Hoffstein V. - Obstructive sleep pnoe reversed by incresed lung volume? Eur J Respir Dis, 1986; 68: Hoffstein V, Zmel N, Phillipson EA. - Lung volume dependence of phryngel cross-sectionl re in ptients with obstructive sleep pne. Am Rev Respir Dis, 1984; 13: Series F, Cormier Y, Lmpron N, Lforge J. - Incresing functionl residul cpcity my reverse obstructive sleep pne. Sleep, 1988; 11: Abbey NC, Cooper KR, Kwentus JA. - Benefit of nsl continul positive pressure in obstructive sleep pne is due to positive phryngel pressure. Sleep, 1989; 12: Strohl KP, Redline S. - Nsl continul positive pressure therpy, upper irwy muscle ctivtion nd obstruc tive sleep pne. Am Rev Respir Dis, 1986; 134: Remmers JE, degroot l.j, Suerlnd KE, Anch AM. - Pthogenesis of upper irwy occlusion during sleep. J Appl Physiol: Respirt Environ Exercise Physiol, 1978; 44: Smith PL, Wise RA, Gold AR, Schwrtz AR. - Upper irwy pressure-flow reltionships in obstructive sleep pne. J Appl Phystol, 1988; 64: Schwrtz AR, Smith PL, Wise RP, Gold AR, Permult S. - Induction of upper irwy occlusion during sleep in individuls with subtmospheric pressure. J Appl Physiol, 1988; 64: Snders MH, Moore SE. - Inspirtory nd expirtory prtitioning of irwy resistnce during sleep in ptients with sleep pne. Am Rev Respir Dis, 1983; 127: Snders MH, Rogers RM, Pennock BE. - Prolonged expirtory phse in sleep pne: unifying hypothesis. Am Rev Resplr Dis, 198; 131: Koenig JE, Thck BT. - Effects of mss loding on the upper irwy. J Appl Physiol, 1988; 64: Horner RL, Mohiddin RH, Lowell DG, She SA, Burmn ED, Longmore DB, Guz A. - Sites nd sizes of ft deposits round the phrynx in obese ptients with obstructive sleep pnoe nd weight mtched controls. Eur Respir J, 1989; 2: Ktz I, Strdling J, Slutsky AS, Zmel N, Hoffstein V. - Do ptients with obstructive sleep pne hve thick necks? Am Rev Respir Dis, 199; 141: Snders MH, Kern N. - Obstructive sleep pne treted by independently djusted inspirtory nd expirtory positive irwy pressure vi nsl msk: physiologic nd clinicl implictions. Chest, 199; 98: Nino-Murci G, Crowe-McCnn C, Bliwise D, Guilleminult C, Dement W. - Complince nd sideeffects in sleep pne ptients treted with nsl continuous positive ir pressure. West J Med, 1989; 1: -9.