The code works well if you remove the last line. Note that y-limit of your plot is 25000-50000. The last line of your code is setting the ylim to [1,130] which doesn't show any of the data.
Perhaps you're looking for
axis tight
r=1.1;
c=1.2;
po=80.;
qo=700.;
rqo=r*qo;
rc=r*c;
t1=linspace(0.,0.2,10);
t2=linspace(0.2,0.8,10);
p1=(qo/c*((rc*exp(t1/rc)-rc)-5.0.*...
(t1*rc.*exp(t1/rc)-rc^2.0*(exp(t1/rc-1.)))+po).*exp(-t1/rc));
p2=(qo/c*((rc*exp(0.2/rc)-rc)-5.0.*...
(0.2*rc.*exp(0.2/rc)-rc^2.0*(exp(0.2/rc-1.)))+po).*exp(-t2/rc));
figure(1);
plot(t1,p1,t2,p2);
ylabel('Pressure (mmHg)'); xlabel('Time (s)');
ylim(gca)
