For you to join those points with a radius that will gradually increase you first need to define what exactly is "gradually increase". For your case, however, it seems that what you want is to fullfill the spiral in a reasonable way, for this you can define an analytical spiral model (check for example: http://mathworld.wolfram.com/LogarithmicSpiral.html), get the parameters that define it and then interpolate in between points. This can be done as follows:
P1 = [36.05,0,20];
P2 = [-43.603,33.523,22];
[th1,r1,z1] = cart2pol(P1(1),P1(2),P1(3));
[th2,r2,z2] = cart2pol(P2(1),P2(2),P2(3));
% Logarithmic spiral Parameters ( r = a*exp(b*theta))
a = r1; % Simplyfication since th1 = 0
b = log(r2/(a))/th2;
thetas = linspace(th1,th2,10);
zs = linspace(z1,z2,10); % Linear z
Rs = a*exp(b*thetas);
[x,y,z] = pol2cart(thetas,Rs,zs);
plot3(x,y,z),hold on
plot3(P1(1),P1(2),P1(3),'r*')
plot3(P2(1),P2(2),P2(3),'r*')
